What an ending. Hopefully the two have some mana potions nearby or else the MC is a dead man. All in all though, this series was a fun read. Time to check out the author's other works.
I think he'll live for a variety of reasons, but the simplest is that she can probably control how much energy she sucs out of him since she's a full succubus now. She loves him, so her relationship isn't a normal succubus/victim one. She's not going to want him to die on her.