[quote=Mtntopview]
Bob cannot kill Unicron, no one can. Not even Primus, not even god himself. Unicron is a force of nature, he exists permanently. He can, however, be defeated.
[/quote]

'everything can be killed'. What, exactly, is death? The end of one's life energy? The failure of the mind? The destruction of the soul?
While Unicron cannot be killed by conventional menas, Bob could wipe out his consciousness. He would become little more than a floating pile of energy and rust, with no will to guide it. Bob could also absorb Unicron, eventually, and turn him into a part of himself. These are just two ways in which Unicron could 'die', regardless of being 'immortal.'