As others have pointed out, the prophecy specifically mentions taking his last breath, and there are ways of being "alive" that don't involve breathing. And not just vampirization, there are intelligent golems, liches, and even some those things Xykon mentioned while talking down V's soul splices. It's all the "unofficial" comments that would have been forgotten that heavily suggest Belkar won't be around at all potential loophole or not. By which I mean on the material plane, but Snarl-death is a distinct possibility for him.