If his house has disappeared and you haven't visited a town in which there were 10 villagers, then he's in your void. Otherwise, your void might have been cleaned.
The void cannot be cleared, your game remembers the last 16 villagers that moved out. If he wasn't adopted by someone else, then yes he is absolutely in your void.
Apollo will be in your void. Your "void" will have villagers that you've moved out in it but haven't found a home, which includes Apollo. If you don't want Apollo to go to anybody elses town, i'd suggest going to a town with 10 villagers. This clears your "void" and it means all the villagers who were in your void are now erased. It's just a little more helpful when going to others towns because most people on the forums don't want to run the risk of getting a voided villager, because they may not want them in their village. Also if you don't want anybody from someone else's void to move in, i'd suggest having 10 villagers or having them clear their void. Note: If you have 10 villagers and somebody else comes over with a void, it'll automatically clear their void. No other villagers from the void will be able to move in since your town would be full.