You are one of the first people i have seen that has mentioned this, it seems obvious but no one has addressed this. If you keep your coins in a wallet off an exchange (recommended method), you will have to quickly figure out how to split the coins/ spend on the new chain, along with everyone else that will be stuffing transactions down the network. Once you get to an exchange (confirmations are going to be interesting) its a race to the order book to sell the coins.

But if you leave them on an exchange that offers 1:1 (not recommended) you run the risk if not actually owning your coins, but skip all the traffic.

this is actually a difficult choice.