I had a similar experience at a previous job, and I was told in no uncertain terms that if the trip was cancelled, the ticket was not to be used.

The rationale was that if the rule was otherwise, employees might find ways to abuse the system by scheduling trips to meetings that would likely be cancelled, thus setting themselves up to "take advantage" of the ticket that - since they "knew" the meeting might be cancelled - should not have been purchased in the first place.

I tried to point out the Dilbert-ness of this logic (is it possible to know that a meeting is likely to be cancelled? If so, why attend, or at least why not buy a non-refundable ticket ...) but that company's equivalent of the pointy-headed manager just stuck to the rule.

For my own comfort in determing ethical / moral / legal questions like this, I try to never do anything that I would be the least bit uncomfortable explaining (not "justifying" or "defending" - just "explaining") to investors, reporters, a jury, or six-year-old children. All of these groups strike me as being able to determine when venal self-interest provided the prime impetus for an action, and for me that's the "litmus test."