Unfortunately, the PA is becoming irrelevant and Hamas is gaining support as a result of the ongoing violence. Old "understandings" between the two on how to handle negotiations with Israel (which Israel was never amenable to) will likely have to be reworked. Officially, only the PLO can conclude an agreement with Israel on behalf of all Palestinians and right now, Hamas is not a member of the PLO. Abbas and Fatah have kept them out. But this will likely change in the future and if Israel chooses to negotiate with the PLO, Hamas will have a say.