Megatron has, at various stages of his many existances, survived:
1) Being nearly killed by Optimus Prime
2) Being rebuild by Unicron (who, according to the comic book continuity, was a god)
3) Falling through a space bridge designed for 1 with a very young and sprightly Optimus Prime(as per the War Within comics)
4) Being consumed by Unicron and later rebuilding himself inside said dead god of chaos and destruction (see TF:Engergon comics).
5) Surviving a year or so in molten lava.
Exar Kun is a silly little girlie man. The force couldn't protect him.