Yes I think regardless of what you can actually do with the ticket if the company purchased it, it is theirs. That said, on what terms did you leave the company? If it was favorable and this ticket has some value to you, you may want to approach you old boss (give him time to forgive you for leaving if necessary, then say you were cleaning out your breifcase, etc and found it) and explain to hiim that you dont thing it is refundable etc and ask if since they cannot use it if it would be alright if you kept it. Who knows maybe he still likes you and you have fulfilled your moral responsibility but still get to go to HNL!