This ought to be the end of the road for Hameed, Burns, Malan, Pope and Buttler. The three older guys should never return. I don't see Hameed coming back. Pope needs to buck his ideas up with a couple of seasons in county cricket.
Batsmen who ought to be in the mix now are Duckett, Libby, Yates, Haines, Bohannon, Joe Clarke, Lawrence, Livingstone, possibly even Vince. Not that these guys are banging down the door with their FC records, but I'd like to see Duckett opening (probably with Crawley) and Livingstone in the middle order as he clearly has a strong temperament for this level. Ideally, one of these guys can step up as a number three. Outside of the openers, they're all number fives.
Bowling-wise, I don't see Broad/Anderson retiring but they won't be playing every Test. Not sure how that frequent rotation helps but there you go. Woakes, Robinson and Wood would all be in the mix - Woakes should only be playing home Tests these days, Robinson needs to improve his stamina, and Wood will still need some careful management. Mahmood is an obvious choice going forward, maybe Brydon Carse as a curveball (he did well in the Pakistan ODIs). There are loads of medium pacers (Coad, Porter, Cook, Fisher) who can take wickets in the CC but probably won't make the step up. I'm very uncertain that SCurran should be in the side unless he's the fourth seamer in a five man attack. Parkinson should be challenging Leach for the spin role, but then I'd feel sorry for the poor guy if Root was captaining. Bess shouldn't be anywhere near the side.
In short, we're not likely to improve quickly. SA will fancy the Summer series.