I'd give this core (with additions) another run next year. I said about 2-3 years ago that their window was 2-3 years, and I stand by that. If they can add a goal scorer, e.g. Tank, and a two-way D man, they can be a playoff contender. A tall order, not impossible. I'd also bring in a better coach, Lambert is avg. Given the scarce talent on this team, they need better than 'avg.' leadership. With that said, if they fall short next year, hang on to that 1st. Whether they succeed or fail (subjective in itself), I'd start the transition next off season.
A mini-rebuild, only sell off certain parts (the old), e.g. Nelson, Lee, Cizikas, etc. We'll cross that bridge when we get there. I would not rebuild this offseason. You have a Vezina-pedigree goalie, just entering his prime, and enough talent in their prime to keep the younger core together, *even beyond next offseason. I wouldn't do a tear-down rebuild either. Besides having an elite goalie, I've said it once, and I'll say it again (and again), they are not fail-safe. A lot of variables have to go right, some of which are out of the organization's control. The onus will be on drafting well in all rounds.
They gave the team likely coming out of the East a strong series. That's with a rusty Barzal, a No-Show Bo, and Sorokin's B game. If they peddle pretty much the same exact roster, they'll likely be a bubble team. A healthy team going into the playoffs could put them in a position to go on a run. Again, with some augmenting, this team could go from a hopeful, to a contender. Perhaps not Cup contender, but 'win a few rounds' contender. JMO.