Hi
I think Betfair will do it for you. This is from their Rules and Regs. Greyhound Racing 12.1
"If a non-runner or reserve runner is declared, then all bets prior to the update of the market on Betfair will be void and all unmatched bets including ‘Take SP’ and ‘keep’ bets will be cancelled"
I also think you will get an error message in the log, something like "invalid market status" because if a market is suspended no cancelling (or any action) can be done.