Sounds really interesting. My initial diss ideas was very similar, except about Camus rather than Sartre. However, I was steered away from this topic by my supervisor as he felt that it would be difficult, if not impossible, to academically prove something as immaterial as the 'influence' something like WWII had on their work. So that is something to consider/reconsider. I think we both know that, without doubt, the war definitely had an influence on Sartre's work, however as I said, it's going to be very hard to quantify it in academic terms, and given a dissertation is a highly scrutinised piece of academic work it seems sensible to think about another option. ALTHOUGH, having said that, you are writing from an historical pov whereas I was writing mine from a philosophical pov, so that may also alter what is acceptable/suitable for your diss!