The injury bug kept the VGK out of the playoffs more than any other factor, since they spent most of the season icing only about $60M (LTIR conspiracy theories notwithstanding), and only started getting the top players (Stone, Pachiorety, Martinez, etc.) back in the last couple of weeks but with them still finding their legs and no chemistry anywhere.
The second factor was DeBoer who has demonstrated an inability to learn from mistakes or fix things, much less rid himself of incompetent assistants, and he's probably sprucing up his resume today. At the very least, there will be an assistant dump and we'll get rid of dead weight there. But more likely DeBoer & Co. is gone, thankfully.
The third factor was in goal, where Lehner was inconsistent at best even when healthy, and never really recovered from his injury (and was really bad when he tried to come back), and Broissoit who could be OK as an emergency backup for a couple of periods, but otherwise was a constant liability.
The fourth factor was, IMHO, trying to work Eichel in and build an offense that has a true star center for the first time in the VGK franchise, which DeBoer appears to be struggling to figure out. On the other hand, if the VGK didn't acquire Eichel, who was able to step in (after he got his legs back) and keep the team close in contention, they likely would have been out of it a couple of weeks ago.
All quite fixable in the offseason, starting with the end of the DeBoer era hopefully. They probably will not re-sign free agent Reilly Smith, who has played little anyway, thus freeing up $5M in cap (leaving about another $3M to clear in the offseason), and that probably means dumping Lehner (another $5M), albeit we may get stuck with a million or something in retention to deal him.
Ironically, Dadonov started playing much better towards the end of the season and finally up to what was expected of him when he was signed, so he might stick even after the aborted trade to the Ducks.
An interesting question will be whether McCrimmon survives, since he was DeBoer's champion, acquired the Lehner/Broissoit duo, botched the Dadanov trade through negligence, and made some other questionable moves. Foley has a low tolerance for failure, and McCrimmon at the very least is on some thin ice.