I don't think the pc would melt the plastic but im not 100% positive on that. Its good that you care about your fish that much and that you will find a much better home than what you can provide for him. :happyfish
A 50/50 bulb is have actinic and half white. If your not tight on money Mh would be a great option for that deep of a tank, plus you could keep alot more different types of corals.
It is a possibility the sixline got to it however fairly uncommon. I highly doubt that hermits did it. Peppermint shrimp are mainly nocturnal and hide alot. At night check with a flashlight to see if it is still in there.
A torch is a LPS coral with a hard skeletal base that it can retract into. An anemone doens't have that it is completly soft bodied and can move around.