In Escape From Aliens in Outer Space, one of the item cards is the Mutate card, which turns a human into an alien. The rules say that the human then plays as an alien from then on. However, if the last surviving human plays that card and mutates into an alien, does the game immediately end with an alien victory, with that converted alien winning as well? We had that happen in our game today, and it felt like an unsatisfactory ending.
As written in the rules book, humans loses only when killed by aliens. Therefore it seems logical that a mutated human wins with aliens even if he is the last one.
Said this, I agree with you, this is definitely an unsatisfactory winning. To avoid it, I suggest you to set as "house rule" that the Mutate card cannot be played by the last human. This will make the human to fight for his life!