If you want a mono export, create a new sequence with a mono Master track and copy/paste your clips into that.
On a side note, there really won't be any trouble playing a stereo file, except maybe for the truly computer illiterate, and even for most of them, it'll work just fine. You really need to have messed up your system ahead of time to hear just one side of a stereo file. That kind of messed up system is not something you can, or should, always compensate for. I say create the stereo, and if someone's system is so glitched they can't hear it properly, it ain't your problem.