De Gea is the one with the most credit in the bank for me but that's only really in terms of how I'll view him after he leaves rather than when I'll think he should leave.
He already has 470+ appearances and multiple years where he was our best player in the bag, so his status was secure however this season went. But realistically if it wasn't for his outstanding shot-stopping form this season I'd already want him replaced, because that's all that's compensating for the many areas he's weak. And if/when his shot-stopping form diminishes again, I'll still want him replaced.
Whereas someone like Sancho has nowhere near the credit in the bank in terms of status/legacy that De Gea does and hasn't even performed as well as him this season, but if I was building a squad from scratch he'd probably make the cut ahead of DDG because I see fewer issues with him when projecting ahead.
So basically the things that give players credit in that sense would be being new arrivals, me thinking there were extenuating circumstances for them being bad recently or me thinking they still have room to improve under the right system and the right coaching. So for me that would be Sancho, Varane, Bruno, Elanga, Rashford, etc.