So I was having a good ol' fashioned random battle in gen 1 with a friend, and at the end, I used pidgey's substitute which got broken by their Muk's explosion. But muk didn't die. Instead he was able to use explosion again after Muk was gone.
http://replay.pokemonshowdown.com/gen1randombattle-684795729
http://replay.pokemonshowdown.com/gen1randombattle-684795729