Nope.
If you really feel this is a big problem for you, don't dice.
People don't forget they bet, and if they did a friendly pm to the user is more than enough.
If let's say 24h has passed, you can pm a moderator to ask for assistance.
If it's really taking a long time the moderator will ban the user until they are back, and if they are on a legitimate sudden leave they are sure to be back in a few days or so, and are sure to ask for an unban with repay.