I think the answer here is going to depend on what your organization and its programmers want to do. If you are in a company with large, complex product offerings used by millions (say, Microsoft, though I have no idea how that company actually works internally), it may be that no one will ever have time to pay attention to the bug that has no steps to reproduce. If you are a smaller shop, it could be that someone will eventually have a little time to sit down and try to reproduce the bug.
Are you in a position where you potentially could try to reproduce the bug and provide steps to reproduce in the bug report? If so, and you have time, you may wish to go that route.
If not, I would at least recommend recording the bug in your bug tracking system (you do have one of those, right?), even if to mark immediately with "unable to reproduce" status or the like. That way, if the same bug happens to the same client or a different client a few months from now, you might be able to spot a pattern that will help the bug get fixed.
Finally, the unfortunate reality is that some bugs will not be considered worth the cost in personnel time to fix. If this bug represents an isolated incident or affects a very small percentage of clients, it may not be considered worth fixing from a business perspective, especially if there is a workaround available.
I hope this helps.