That is interesting. You killed a mighty urkan, feel proud.

EDIT: Tried out myself, they don't seem to come back.. They die permanently.

Seems a bug to me, Urkans shouldn't be allowed to go on ice.

Savefile: Mykara - Kill the Urkans.sav

EDIT2: Even more interesting, you can put the mighty Urkan on a ship if you reserched shipyard already before the end of the winter...