Interesting question. I know that normally not having a ticket on a normal visa is not a wise decision, but I don't know for a student visa. Personally I wouldn't risk it, if you can just buy a 100-150USD ticket to HK. It's not so much Taiwanese immigration, it's more the check-in clerk at your outgoing airport won't let you through. They can be very strict about it. I can see you saying "but I'm on a student visa" and it falling on deaf ears. They might not know or care.
But I could be wrong.
On the other threads people mentioned refundable tickets, or "ghost tickets"- can't remember the exact name.