This is true.  Those accounts will have a negative balance.  If the missing coins are never repaid, I will cover that loss with my own coins.

The procedure I ran to rollback the fake bets was:

1) work out how much each investor gained by the fake bets, by considering what percentage of the bankroll they represented for each of the bets.  this percentage changed as the bets were made
2) if the investor's balance was lower than that amount, divest enough coins to make the balance big enough, if possible, else divest all
3) debit the account with the amount gained from the fake bets

So you may find that the bets have been taken from your balance rather than your investment.