The dead servers are skipped in the block production.
On your point about dead voters votes, yes, you are 100% correct.
There are so many dead voters votes out there in this pool, that if this was a real body of water with that many dead fish in it we would have a biohazard disaster on our hands!
Thanks @jackmiller. I just found out one of my witness votes is marked with a red strikethough. I think that means they are inactive, yet I noticed they continue to promote the witness on all the recent posts on steemit. I took the initiative and researched, and contacted them on discord to find out why they are campaigning for witness votes without an active server.
You can tell if they are dead or just temporarily down for maintenance by looking at their last produced block time and lets say their price feeds.
If they haven't done either of the two in a long time, there is a very good chance that they have resigned.
The best approach is to do what you did, ASK people up front!