Hook is in Storybrooke for one reason and one reason only, to get revenge against Rumple.
Once that Story arc’s been and gone, what then for Hook? Keep him around as potential love interest for Emma even though we know she’s not going to let him near Henry? THey could do that within season 2 whilst Hook still has purpose in Storybrooke.
When Hook leaves Storybrooke (whether that’s by being killed off, being banished to another realm or just travelling and exploring our world), he doesn’t necessarily have to leave the show per se, he can still appear in flashbacks like Graham. With them bringing in new characters each season, it’s also likely that Hook has crossed paths with plenty of characters and will appear in their stories so he’s not going to suddenly cease to exist.
All magic comes with a price!
Keeper of Felix