If the old one doesn't die for some reason like with Ethereum Classic than it is the same as with Bitcoin Cash and Ethereum Classic itself, so you can have a bet on if it you want.
It seems extremely unlikely that the old chain doesn't die. For the old one to continue, there has to be enough Ethereum miners and users that disagree with the HF to continue to maintain the status quo. Afaik there isn't anyone in the Ethereum community that isn't looking forward to Metropolis.