So it looks like we are three. 
In which case, there are two options:
1. hand-wave the conclusion to this and reset the game, returning the party to town. 
2. play out this story with the three PC's and Walter. I would rather not have three NPC's, but if you want to keep the party together and take on the responsibility for running them, we can do that.
I both cases I think that there will be some re-recruiting at some point. 
No one has expressed any preference for the options so far. So, where to from here?
thotd