There is a very basic problem behind that: A respawn is NO entity on its own therefore its impossible to trigger the respawn. You can only activate/deactivate the whole entity.
Mo idea if this actually works but its an idea for the creature main script:
state=0:timerstart,state=1
state=1,timergreater=10000,destroy,activate=0
If the spawn is destroyed and the entity deactivated in one go it should wait to be triggered again by a switch.
Of course the entity is destroyed even without the player killing it so its use would be limited even if it works :/
In case you find my grammar and spelling weird ---> native German speaker ^^