This question depends on how well Dark Phoenix would’ve done critically/commercially.
A more interesting phrasing of this question is what would happen if the main franchise was as consistently critically well received & popular like the MCU and never had a badly reviewed movie before Disney bought Fox?
Consider what Kevin Feige said about Deadpool’s move to the MCU
: “When we were purchased, Bob said to us, ‘if it’s not broke, don’t fix it. There’s no question that Deadpool is working, so why would we change it?”
This comment is telling in a lot of ways, and gives us a window into Feige’s thoughts on the state of the Fox Marvel properties at the time.
1. Notice that he
only says this about Deadpool, not the other Fox Marvel properties like X-Men & FF.
2. This indirectly reveals that he only views Deadpool as the one Fox Marvel franchise that’s working well enough that it doesn’t need the “start from scratch” hard reboot that FF and X-Men will get. Side note: I mention Deadpool separately from X-Men
since it isn’t part of the X-Men license.
3. Feige made these statements before Dark Phoenix was released, and knows full well of the inconsistent quality of the Fox X-Men movies. Logan came and went but the last mainline X-film before DP was Apocalypse a stinker that left a bad taste in a lot of people’s mouths.
I point all this out to stress that I don’t think Feige would automatically be swayed to keep the Fox cast or even bring those versions into the MCU continuity like he will with Deadpool just because one movie in a franchise with varying quality throughout the years performed well. Well...not unless it made a billion dollars and had incredibly good reviews which wouldn’t be possible with a movie coming off the bad buzz of Apocalypse &
under the helm of weak talent like Simon Kinberg.
Let’s say Kinberg pulled off a fluke and the movie turns out half-way decent and it’s better reviewed than Apcalypse(let’s say it lands in the 65-75% range) and did about on par with the last movie or slightly better than Apocalypse in part due to better word of mouth helping it. Then I’m sorry, that still wouldn’t be enough to signal to Feige to not change things with the X-Men. Even in that alternate timeline where Dark Phoenix worked(kind of) Feige still likely does what he’s doing now - which is putting the X-property in hibernation, while he plans a drastic refresh of the series.