10 TRAGIC Predictions For Avengers 4
6. Banner Loses Himself Completely
Before Thor: Ragnarok came out, Mark Ruffalo revealed that his character was about to embark on a three movie arc that would end with Avengers 4. Given that we now know that this arc is defined by issues of control and the internal battle between Banner and the Hulk, it makes sense that that conflict will come to a head in the coming sequel.
The happy ending, would see Banner and Hulk co-existing in harmony, but that would set up a Hulk solo film for Phase 4 (or at least hint at its possibility), which probably isn't an option for Marvel. The old rights issues involved in that one still apparently persist. So no happy ending for Banner.
It could also be that Banner takes control of Hulk entirely and is "cured" - which would certainly be within the powers of the Reality Stone (and would also be an easy way for Thanos to neutralise him as a threat). But that doesn't sound quite as fitting for Thanos as the alternative - letting Hulk win in an attempt to ingratiate himself to the creature.
Since we're partway through this arc, it seems that - even if that victory for Hulk isn't permanent - we'll see Banner go through something terrible in Avengers 4, losing himself for a while at least. And given that that is his biggest fear, it's hard not to count that as a tragedy.