If you opened a long position at 4.30, your position is closed at 4.30.
If you opened a short position at 5.30, your position is closed at 5.30.
Using this approach, the only loss for customers will be opportunity cost. Sounds reasonable?
Personally I think that how would any other company would decide, simply cancel all orders. But longs will be pissed, at least they should get their balances in BTC if they had them in BTC.