What I do know is that Marcedes is having issues with their W13 and this should not be a good season for them, so I would patiently wait for the end of this season before jumping to conclusions.
Gasly has been loyal to the Red Bull family for a long time, but the 25-year-old Frenchman has always been very outspoken about his expectations, and it's clear he's looking for more recognition from Red Bull and feels he's ready for a second chance in the car as he side of Verstappen.
I still think that veterans would be a lot better for this second driver position but either they have too much of an ego to try that, or they just do not think about it. Perez is way too good to leave him be, but imagine if vettel worked hard to bring Max a championship? That would have been awesome.
Would anyone want to go to Mercedes at the moment? Ferrari and RB would be the teams of choice. I suppose the big question is if at the end of the season the Merc is still not up to speed, then will Hamilton want to try a different car before he retires? I'm sure he'd want to drive a Ferrari at some point if it turns out Sainz is not quite as good as everyone had hoped. But I think the chance of Hamilton at Red Bull is about zero, really can't imagine him in a team with Max, it would be like the Rosberg years again but about 10x worse!