We can't get Donnarumma.
There is some cultural thing, how Spanish players will always pick Real or Barca as their firts choice.
How Germans will usually pick Bayern over other teams.
How Brasilian superstar Cfs will pick Real/Barca over other.
About (top) Italians, they are the same as Xavi/Iniesta/Puyol, Spanish or German guys.
They won't leave a country unless the club forces their exit, or if some insane bid comes.
More or less all Italians play in Juve, Milan, Roma or Inter. Verratti is more or less the only exception.
Playing in Juve or Milan is like playing at Barca/Real for other players.
Donnarumma, I can see him only staying at Milan, going to Juve or in some insane case to some foreign team who will pay like 100M.
De Gea is a Spanish.
He wants to come back, this is his culture, his home, his league, his climate.
He is quite a realistic option.
Curtois is less realistic than De Gea, since Spain isn't his default home, but he lived here and he is willing to come back.
My personal estimation about availability of these 3 mentioned Gks for Barca's transfer:
1. De Gea 80%, for a 50+ M fee
2. Curtois 50%, for a 50+ M fee
3. Donnarumma 5-10%
About Mats, if he'll continue to play like this, we have all learned a nice good old lesson:
"Don't fix what ain't broken"
This spring and summer (2016), majority of people here were constantly saying that Bravo is NOT a better Gk anymore, and that him and Mats are almost on the same level.
And since Mats is younger, this choice was supposed to be a no-brainer.
Well, it seems that majority of us are realizing that Mats is surely not on Bravo's level.
Who knows, I would personally take Bravo back next summer (if he'll have problems at City, for example).
Anyway, a good old video when we actually had a safe Gk, who wasn't showboating, who wasn't trying to please the crowd, who wasn't creating chances for our opponents out of nowhere with his dribbles and passes, and who wasn't trying to be the next Neuer, but who was=just himself:
https://www.youtube.com/watch?v=7jNUggjWkXg
A guy who was never loved by our fans (how much he deserved), mostly because he was old, and people never considered him as a long term option. (A keeper whom we can have for a next decade
). Oh, well...