If he's not wandering around on the boat and you want him specifically, then I can't think of anything else to do besides 1) reloading a previous save before getting on the boat and trying again to resurrect him, 2) reloading to a save before he died and replaying progress, or 3) restarting the game.
However, there's a lizard on the boat, Sgt. Zrilla, from whom you can hire mercenaries. They won't have any companion quests, but will fill out the empty spot in your party if you only care about the build and not about Ifan specifically.