I think what's noted above is important; you acknowledge and make it clear that the character is very potent, and make it so while the char does not get killed outright, coming back may be quite difficult. In the case of my own demons (which, admittedly, are far from acceptable for most roleplays on this site), their defeat often results in them being incapacitated for up to a few hundred years as they respawn in the Abyss to recollect enough power to return to their natural domain with similar power levels as before, and even then, it may take a while to make a solid actual connection to the mortal realm.