Since characters are stored server side, there is no way your system update has anything to do with their disappearance. Best thing to do would be to contact Blizzard.
____________________________
People don't like to be meddled with. We tell them what to do, what to think, don't run, don't walk. We're in their homes and in their heads and we haven't the right. We're meddlesome. ~River Tam
Sedao