Preserve would basically mean to keep it alive.
Now, I understand that this is asking a lot, but there are other franchises that had this happen to them. Basically, the franchise at hand is kept and being told about to the point where, years later, they finally give the franchise it's proper ending.
Look, we all know that 13 was a disaster! (Heck, some of us are convinced it doesn't exist. It's that bad.) We don't want that to be it's end. None of us do. We want one last good movie before it truly kicks the bucket. So our best bet to get something like this is to keep it alive and growing in fan culture until we finally get it.
Look, I know it's asking a lot, but it can be done.
So, how would you go about preserving this franchise?