Think it should cost 2|2; if your opponent doesn't have a shield maggots are very powerful, but against a 1DR Shield they're totally useless, while condor/vulture is quite good.
"Necrophilic" is a passive ability and cannot be lobotomised. If he wants to discard the maggot, its owner must first sacrifice one of his creatures. I suppose red circles will appear on the creatures when you click to discard the card. If he cannot sacrifice a creature (because he doesn't have any in play) the owner must sacrifice 10 HP.
It's very situational, but I think 6/7 HP is more balanced.