How can I get a mob to despawn

Basically I got into a sticky situation in a cave with a mob and I want it to despawn. I am logged out. I don't think I can survive if I log back in, and I have valuables. If I die, I don't think I can easily retrieve items, I have terrible navigation.

It's multiplayer but I don't want to ask other players to do anything

I want to log on safely soon... what can I do?

Thanks!!