make it respawn after you leave the area and go back in. (not via dragonstone, tho)
this is the most likely usage of respawing mops in the a-rpg genre, if used at all.
everyone can decide if they want to level up and kill the mobs again or not. yet you can still explore everythiung and take your time while visiting it the first time.
the krähennest (crow's nest) is the only area that should have respawing mobs by default [that is, until you destroy the engineer of course], BUT increase the spawn timer a bit.
an option isn't needed, nor a must have, it destroys the level up system.
I'd have some other balancing tweaks that I would like to see, but i doubt they are important enough to make it into the game.