If he plays 40 games per season which should be probable, then he's coming back as 21 year old with good enough experience to fight for 3rd/4th CB spot, we will probably have one world class CM we buy this summer, then Smalling, Bailly, perhaps Lindelof and offloading injury prone Jones and Rojo in the meantime, could be a good timing for him, with Lindelof not really convincing season, Bailly still being injured here and there and Smalling solid great CB but not the best playign from the back, he should get that chance, especially if we have a new manager and I believe it could be some former player or McKenna.
If he's not ready he could play for Villa who might be back in Premier league at that time already, or other team in the first division for another season and then he would come back as 22 being definitely ready to push for some serious gametime. He could even spend another three years on loan from now and still be very young to have a very long career with us if he comes back, so fingers crossed he stays injury free and get plenty of gametime... he's got it in him to be a top half premier league player and a team who gives him chance like now Villa could have a bargain, if he's considered not good enough or they manage turn his head.
Thanks Brucey btw!