From the rules:

"Once any character has reached the Crown of Command, any character that gets killed is out of the game. Note that this rule stays in effect for the rest of the game, even if a character leaves the Crown of Command."

How character can leaves the Crown of Command?

"When a character is on the Crown of Command space, a character does not move but remains there instead. Characters on the Crown of Command
cannot turn back."

If he is killed by other character then other character will stay on Crown space.

Thanks

Transference Spell allows another char on the Inner Region to swap places with another char on the Inner Region (usually the other char is on the CoC).

Path of Destiny Spell forces a char to take a Warlock's Quest, and they must complete the Quest if possible (so if they get a Discard 1 Follower and they have a Follower, must discard), at which point you're teleported to the Warlock's Cave and get a Talisman.

Ice Queen ending offers a choice of leaving if you lose against her and roll a certain number.

Those three off the top of my head.

You can also use the Vortex spell from the Frostmarch expansion. You can create a warp gate, that will teleport you to a other space somewhere on the mainboard.

The text allows you to use it on the Crown of command.

Also the Magic Portal(from frostmarch) can get you out of the Crown of command (end space)