Gilead managed to demonstrate how curing a major disease does not result in such a spectacular outcome (of the trillion dollar scale). They did very well by curing HepC, briefly, and now they're eroding back down after just a few boom years. The same would occur with curing HIV/AIDS. There would be a brief boom derived from sales in some developed nations (most nations would receive the cure
extremely inexpensively, as with HepC). It might get a company to a couple hundred billion market cap short-term, nowhere near a trillion dollar outcome however. Further, attempting to charge a lot for the HIV/AIDS cure (such that you could get to a trillion dollar market cap), would result in a far worse PR outcome than what Gilead & Co. saw with HepC drugs; calls for nationalization would be overwhelming. Nations such as India and China would simply ignore all patents and proceed to copying the cure - few would support any economic counter/consequence against that move.
It is often said that companies would intentionally prefer not to cure major diseases. Then Gilead (Pharmasset), goes ahead and does so, while charging less for the cure than the cost of healthcare for living with HepC (much less all that is lost from HepC, including quality of life and economic contribution) - and for doing so, they were treated as a villain due to what they charged. For such reasons, I doubt we'll ever see drug prices high enough to deliver trillion dollar outcomes. Throw on top of this, that the last bastion of crazy drug prices - the US - is nearing an end on its tolerance for such.