I mean if Wells is allowed to stick around that just means Marvel is fine with losing money on the table. Don't think that's a good thing to advocate for.Quick adjustments are rare if we're talking about a new direction and creative team for a flagship book. Look at how much time passed between Tom Brevoort being announced as the new X-Men editor and the releases of the creative teams for the new titles (and those are still a few months away.)
It's entirely possible Wells is wrapping up his last story. He said he wanted to book for about 2 1/2 years/ 60 issues and the current stories have a tying up loose ends vibe. In this case, Marvel probably has a new creative team ready and they're working on their next comics.
But we might have it wrong. Maybe Wells isn't planning on going and wants to stick around until at least Issue 1,000.
Marvel has solicited a Spider-Goblin story by Ed McGuiness that ends in July. There's probably a few issues of art already completed for a follow-up story by John Romita Jr (due to the twice-monthly schedule of Amazing Spider-Man, even prolific artists like him would have to get a head start on a longer story.)
That story would take us to October.
If Marvel decides they need a new direction and creative team, there are several ways to handle it.
The most excessive would be to cancel everything that hasn't been published, and get a new creative team ASAP. In that situation, they're going to have come up with new material fast, and some of it will likely be filler because they're not going to come up with a long-term plan in one weekend.
Not quite at that level would be telling Wells he's fired and that someone else will finish all his scripts. They could do it, but it'll likely upset other writers and artists.
The most civilized way to do it would be for Marvel to tell Wells that they've decided to go in a different direction, that someone else will be taking over soon, and that he'll be able to finish the stories he's currently started with a few issues or an annual to tie up loose ends. Sometimes writers walk away under these circumstances, but Wells doesn't seem like that sort. An advantage here is that it also gives time for the next creative team to get ready. But assuming it'll take six issues to wrap things up (in a scenario where Wells wasn't planning on doing that) we're not going to have the first issue of the new creative team until November. If Marvel made the decision today, it would probably take six months to implement.