I believe that if they emphasize him as a love interest for Emma then he might be cast off too easily (if say for instance the love interest arc ends) but there is a lot of possibility. Really what I like about this show is that there are a lot of possibility for all characters. Look at what they have done with Grumpy, Rumple, Belle… and there is a lot of history he has to come to grips with his past (his piracy, his being in neverland, his revenge–whether it was for pride, his lost hand or milah) and possibly more that a few good moments might not help. Not to say it can’t happen but it all depends on what Hook wants really and if he will have a “loved” (possibly Emma) one to give him the bit of humanity that Regina and Rumple have to soften their villainy…
Hook does show a lot of promise. As long as there is a good story to tell I do not mind him staying on the show.