I had this happen to me once - I left a company after they had booked a lot of us to travel to LHR for the annual corporate gathering. The ticket was on VS economy and when I left, since I was no longer attending the event, the ticket stayed in my name but the company asked me to reimburse them for the cost (about $675 IIRC). Kinda tacky but also, kinda necessary from the company's point of view. I never did use the ticket.
So sounds like the lesson is to say I'll pay for the ticket only after I use it. So if I don't use it, it just expires unused. If I use it, I pay the company. Why should I assume the risk?; this was a company expense.
Or if I am to assume the risk, then I'll pay only N% of the price at the time of termination. Or just refuse to pay anything.