He can always come back but his regeneration can be lengthened or held off. He’s effectively dead until he regenerates, so he’s more like “infinite lives man” rather than strictly immortal.
Someone would likely need to figure out how to erase all his cells from existence simultaneously to permanently put him down. (He can regenerate from “soup”)
Sounds like the Maulers need therapy for their inferiority complex … imagine them without the clone insecurity (less funny though)