More like, it got merged with Eliza, sort-off like Cell Fusion.
And as Renka said before, when cards die, they aren't dead in true sense, because they just return to the "Mother Sea" and get reborn later.
Cards are immortal in a sense, they just discard their current body and later return with a new body.
Though Named Cards aren't like that, because if they die, they get trapped in a limbo, making it impossible for them to discard their body, nor allow them to return to their origin. They can be revived, but only by their contractor who named them.
So basically they could be stuck for life if their contractor dies as well.