There's really not a lot of doubt about Vandoorne's talent, but I am very curious about Stroll..I mean, F3 hasn't been very competitive in the past two seasons (no exception talent or something) and it's mostly because of his billionaire father that he will be in F1 already next year Not seeing he doesn't have what it takes, clearly he is talented, but I doubt he is already good enough..
It will be weird to see F1 without Button, he was in F1 for almost 2/3 of my entire life and I can't imagine a season without him, one of the nicest guys on the grid and one of the most calm drivers out there Massa on the other hand..nah, I won't miss him for a second to be honest.
You forgot to mention Nico Hülkenberg has signed with Renault for next year, leaving a place open at Force India and one place left at Renault. Likely candidates for the Renault spot are of course current drivers Magnussen and Palmer, but they might also try and get Ocon or Wehrlein. I would be very surprised if the now open Force India spot doesn't go to one of the two Manor drivers because of the Mercedes connection, both drivers being in the Mercedes program and they're simply very talented (especially Ocon).
Hopefully all this moving around means that the arguably biggest talent of them all (looking at the classes with young drivers), Antonio Giovinazzi, will get his chance in F1 next year, he absolutely deserves it