They should bring him back, have Rick Jones get Phil a copy of his old goblin gear.
Towards the end, Phil was getting pretty good, and his powers stemmed from chemicals he was dipped in, and his mask. Firestar--I'm assuming we're talking about Angelica Jones of the New Warriors/Avengers and Spider-Man's Amazing Friends, has great control over her powers, but because of her years of having to hold back, I think, is not fully developed in them--close, but she's always had to hold back, and I think there would be a bit of a psychological handicap there--self-imposed limits that didn't just up and leave.
I think it's pretty even, about 6/10 or so, Firestar in favor because of her experience.