Assassin was given a set amount of mana by Castor so in the original FSN anime he disappeared before she died. I don't think he appeared after his initial appearance in the UBW but it's been a while since I saw it. However, it depends. As they explained, servants can live without a supply of mana for a certain set of time. That means it's possible that he's still there guarding the temple, but like I said, I'm unsure. Plus I'm not caught up with the anime right now (I'm an episode or two behind) so I'm just making guesses.
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