That really is a good question. As far as I remember, the solutions have been short-term fixes. In IH #377, it seemed that the two ascendant personas at that time (Savage and Joe) agreed to help out Bruce for the greater good. As we discovered much later, Bruce subconsciously created a fail safe (Savage Banner) since he believed (I am postulating) that the merger was only temporary, and eventually he would lose it. Now, with Joe restricted to the Banner form, it makes me wonder--how much control does Banner exert over his personalities? He can suppress them for extended periods of time (e.g., Devil, Savage, Joe) yet he can choose which form he or they will be able to use (again, Savage "Banner", Joe "Banner", a Bruce-controlled Savage Hulk). It would be interesting if Ewing could explore or address this aspect. Any thoughts?
Plus didn't Banner tell Tony, after Tony used Extremis to fix Banner after he was shot in the head, that it depends how much intelligence he channels into the Hulk?
Also at the end of Pak's run, wasn't it confirmed that overall Banner and the Hulks protest too much and that Banner has more control then he lets on, its just that Banner is such an unstable headcase that really affects the Hulk?
also Pak did drop the implication that Banner knew in advance what gamma could do hence he was prepped to survive gamma and also an implication that if Banner didn't become the Hulk that Banner would become evil/insane?