I don't believe he has the appetite to commit to the county grind which is what he'd need to do to earn his place back - he wouldn't just walk back in having played nothing but T20 cricket (and mostly badly) in 18 months. Moreover I don't think there is room for him in the Test team anyway. Trott might get back in as a makeshift opener for a couple of years purely because we don't have many other candidates and there has been an ongoing vacancy there in effect ever since Strauss retired. Bell bats 4 and Root bats 5 so where is KP meant to be going?
Would he get in the ODI team - yeah, probably. Although he was largely dirt in ODIs for years before he flounced off. But he isn't going to be around in 2019 so really, what is the point.
Not strictly true, averaged over 40 in ODI's across his career. Compares well against Bell (37), Morgan (36), Root (40 exactly), Strauss (35), Cook (36), Collingwood (35). Trott is the only English player with a higher average in ODI's than KP. Also, only Trescothick with more hundreds than KP yet only averaged 37 himself.
Pietersen would need to prove himself in county cricket, and with Surrey being in Division 2 he could easily blast a load of runs at the start of the year against some of the bowling down there. Depends on how serious he is about playing for England again.
The problem with Graves' comments have now ramped up the pressure on Englands batsmen. Following the World Cup we go to WI, before NZ come here and then Ashes this summer. If KP does go and score county runs, anyone failing in either the test or ODI sides will face massive pressure from pundits and public to get KP back in the side