I think Villa will be a Europa League/Challenging for CL team within 3 years without Grealish, and next season with him. They were 6 points behind the race for 3rd/4th for most of last season with 2 games in hand until Grealish and some other key players got injured - there's a decent chance they finish 4th if he stayed fit.
They have a lot of ambition, a very good manager and are putting a great squad together.
The Premier League's "middle class" of Leicester, Everton, Villa, Wolves is stronger than it's ever been before, and with some of the old elite, ie Arsenal, Spurs tripping up, there's going to be real competition for the Europa places.
So I think there's more incentive to stay at one of those clubs than there was a few years ago.
Still think Grealish will leave though, or try to at least.