The organization has proven they will and can change anything they want. I think they will always hold on to 1914 with significance. You probably nailed it on the head as it will always be when satan was cast down. I don't think (and I admit I could be wrong tomorrow) they will have to do any significant change until after 120 years has past from 1914. Jaydubs will grasp at anything to make it appear they fulfill old prophecy today. Every JW would gladly hold onto the 120 years of noahs day. Once that goes they will have to create something new. I have no doubt they will create something new and do it successfully when the time comes.
JWs will always say that people should have waited on Jehovah when it comes to people disagreeing with the organization. So even if thousands of people were DFd over 1914, most JWs would shrug that off as those people weren't humble and should have waited. An elder told me a featured video coming up on JW TV is how to explain 1914. So if that happens I don't see them having any plans of changes soon.