IMHO the votes should only be rescinded if the proposal dies and reopens (not formally, I just mean through neglect). In that situation most people would come to it with a new perspective, but votes from the judges who haven't been around would still be counted even though, if they'd been there, they'd probably change their minds.
I don't think a proposal that's sitting idle should ever be suddenly reactivated because a vote expires (for one thing, somebody would need to be monitoring the old proposals in order to notice!)
As a separate issue, I think having separate rules for "proposals expire" and "judges' votes expire" is too complicated. The voting system is already pretty complicated.
So I think I'm leaning towards simply expiring votes that don't get a resolution (which would automatically expire votes of judges that aren't around anymore). That only leaves the situation where a judge casts a vote, then vanishes, and while discussion drags on a lot of new points are raised (or new material comes out which changes the situation) and so the remaining judges think that first vote should no longer be valid. In that case, we can always make a specific proposal "ignore JoeNotCharles' vote, he hasn't been here for months and missed most of the discussion".