Okay, so the second half of Gretzky's NHL career would be 1989-90 through 1998-99, right? So, we're imagining he was born in 1971 (like Sundin, Bure, Nedved, Weight), so he's 18 or 19 in 1989-90 and he's only 27-28 in his final season, 1998-99.
Thus, we're looking at a extremely talented and amazingly productive player who either had a career-ending injury at age 28, or who lost interest in the sport and decided to live off his investments and play golf every day from his late 20s.
That is, he'd be remembered now either similar to Bobby Orr minus the two Cups---wherein his career was sadly cut short by injuries; or similar to Jimmy Carson---wherein he was just not that into hockey and peaked very young. In one narrative, he's a romantic figure (probably the poster-child for ending violence in hockey), and in the other he's an eccentric.
We're assuming, I guess, he's still a small-town Ontario boy, but now he's drafted by the L.A. Kings and later (aged 25) signs with the New York Rangers. (I think we can assume he doesn't go to St. Louis at all, as the Blues would have had to give up a lot to get him at age 25.) So, let's say he had seven seasons in Los Angeles, and three in New York before the career suddenly ended.
Anyway, this is more-or-less how his career stats pan out, going by 'adjusted stats" (to 'correct' for the downward scoring totals as the 90s' progress) on Hockey Ref., and with scoring finishes, etc.:
1989-90 (L.A.)
120 points in 73 games
-- 1st in scoring (Art Ross). He's the first rookie in NHL history to do this.
-- 2nd team All Star (though I wonder if this might have been 1st with his 'rookie' narrative)
-- 1st in assists (2nd or 3rd highest total of all-time behind one Mario season the year prior and Orr 1971)
-- wins Calder trophy (over Makarov, Modano, Roenick), probably with 100% of the vote
-- probably finishes 2nd or 3rd in Hart voting (as opposed to 4th in reality)
-- in playoffs, fourth-place L.A. upsets Cup-champ Calgary; in the second round Gretzky is hurt vs. Edmonton (the first of many accumulating injuries in his short career to come)
1990-91 (L.A.)
146 points in 78 games (similar to McDavid this season)
-- 1st in scoring (Art Ross) by 28 points. His 146-ish points would be 2nd-highest all time.
-- 1st team All Star (the big talk during this season would be: "Is young Gretzky better than Mario??")
-- 1st in assists (his 109-ish assists would be the most all time, by far)
-- wins Hart Trophy (Brett Hull would still get his share of votes, but with L.A. finishing in 1st for the first time, and with the massive hype over Gretzky from the previous season being matched with reality, I have to think 20-year-old Wayne wins this.
-- in playoffs, Kings choke slightly vs. Edmonton
Canada Cup 1991
-- Canada wins, with Gretzky leading tournament in scoring. As a 20-year-old, maybe he doesn't get injured in the second game of the final series (?). If not, he wins tournament MVP in a landslide (as he should have, anyway). But we have to assume he's still 'Suter-ed'; hence the drop-off from next season....
1991-92 (L.A.)
108 points in 74 games
-- 3rd in scoring (1 point behind Stevens; 8 points behind Mario)
-- 1st in assists (albeit with nearly 30 fewer than the previous season)
-- L.A. underperforms in the playoffs again (narrative begins that maybe young Gretzky can't "lead" his team, as well as rumors about the severity of his back injury)
1992-93 (L.A.)
52 points in 45 games
-- Bummer season due to injury, with Wayne taking a back-seat to much older players like Robitaille, Kurri... However:
-- In the playoffs, the Kings surprise everyone by winning the West and going to the Cup Finals. Gretzky leads all players in goals, points, etc. His 40-point playoff is the second most all time.
1993-94 (L.A.)
119 points in 81 games
-- 1st in scoring (Art Ross)
-- 1st in assists
-- 1st or 2nd-team All Star (not sure how this plays out vis-à-vis Fedorov's big season in Detroit)
-- L.A. has a massively disappointing season, missing the playoffs entirely. With McNall going to prison in summer, rumor begins that Gretzky, only aged 23, wants out of Los Angeles.
1995 (L.A.)
about 50 points in 48 games
-- 19th in scoring (behind Owen Nolan); 9th in assists (behind Joe Juneau)
-- L.A. tries to get physical with new players, but crashes and burns again, missing the playoffs. The new talk is that Jagr and Lindros are better young players than Gretzky.
1995-96 (L.A.)
97-100 points in 80 games (his pace dropped a bit in St. Louis, a trade which I'm assuming doesn't happen here)
-- around 10th to 11th in scoring
-- Kings are now heading toward a rebuild without Gretzky, who is clearly on his way out once this season is over
World Cup 1996
-- Gretzky plays, is okay, but Canada loses
1996-97 (NYR)
101 points in 82 games
-- 4th in scoring
-- 1st in assists
-- 2nd-team All Star
-- up-and-down season in New York, but overall the narrative is that Gretzky has had a minor renaissance in a new environment
-- Gretzky appears in the playoffs for the fifth and LAST time in his career, doing extremely well, though the Rangers falter against Lindros and the Flyers in the third round.
1997-98 (NYR)
103 points in 82 games
-- 3rd in scoring
-- 1st in assists
-- 2nd-team All Star
-- Rangers have a horrible season, scoring just 197 goals and missing the playoffs
1998 Olympics
-- Gretzky plays, but is somewhat disappointing.
1998-99 (NYR)
70 points in 70 games
-- 33rd in scoring
-- Gretzky scores over a point-per-game through 58 games, but after a late-season injury, he phones-in the remaining 12 games, knowing he's going to retire.
(Retires aged 28.)
So, Gretzky would retire with 10 NHL seasons (one a half-season to injury; another a half-season due to NHL work stoppage), and so the game-equivalent of only about 9.
His final career numbers would be:
713GP (56 more games than Orr; 47 fewer than Lindros)
968 points (so, 1.36 PPG)
He would retire averaging 112 points per 82 games, over ten years.
Career accomplishments (adjusted):
-- 2nd-highest season point total ever (146 points) [though McDavid may threaten that this season]
-- Highest assist season total ever (109 assists)
-- Six times 1st/2nd-team All Star at center
-- 1 Hart trophy (probably three times a 'finalist')
-- 3 Art Ross trophies (7th most))
-- Playoff leading scorer 1993 (2nd highest playoff point total ever)
-- Calder trophy (highest scoring total ever)
His regular season career would be looked back at as being an unbelievably great first two seasons (very similar to Wayne's actual first two seasons in Edmonton, but in a major US city), followed by a dominant Canada-Cup performance, and that brief period in spring to autumn 1991 where Gretzky would have been tipped as the new superstar of hockey, threatening Mario Lemieux's status as the game's greatest player. However, he would equally be remembered for his subsequent decline in what should have been his peak years, esp. from autumn 1991 (age 20) to spring 1996 (age 25)---despite a run to the Finals in '93 and a scoring title in '94---and his bitter fall-out with the Kings' organization. He would be seen to have had a minor resurgence with New York for two seasons, but then an ignoble final year.
His playoff resume would be mixed. Only five appearances in his whole career, but with one run to the Finals and one Conference appearance, with him being heroic in both. However, his 1991 and 1992 playoffs, with a solid Kings' team, would be remembered as fairly poor (although he was only 20-21 years old for those). With his last two playoff appearances (1993 & 1997) being remarkable, I think a retrospective narrative would emerge that his teams in his 'mature' years really let him down, and that if he had played on better clubs from around 1994 to 1998, he could have done a lot more.
We'd probably be talking about him now as the great "what if?" of hockey history, along with Orr and to some extent Mario Lemieux. But his status as one of the game's most gifted players would be secure, and his peak (c.1989-1991) would be seen as one of the top three or four in history. His team success would have been very small, however. Aside from the 1990-91 season and the 1993 playoffs, none of his clubs would be remembered for being very good. To what extent he would get sympathy or blame for this in the 'grand narrative' would probably depend on the extent his accumulated injuries were seen as having caused his premature decline and early retirement.
But what stands out about his inconsistent career is no fewer than SIX 1st/2nd-team All Star selections (at center, no less). That's obviously a slam-drunk Hall of Fame career.