If unexchanged balance just grows over time, you're not getting paid accordingly.
Has your fear ever been realized here? Except for the occasional server problem, has there ever been a failure to convert the unexchanged to exchanged?
There have been frequent occasions when the unexchanged built up during the day, but somehow, we all manage to muddle through and, at the end of the day, get paid.
Stop buying problems where there are none. Everything will be just fine.
Past performance is no indication of future behaviour. It doesn't help you to close your eyes, stick your fingers in your ears and say "nononono I can't hear you, everything is fine".
Okay, Chicken Little, you just keep worrying for all the rest of us sane folks. Talk about a waste of time and energy . . . worrying about something--which has NEVER happened--suddenly happening.