BTC is now the base.
Most of the exchanges have BTC as prime currency to trade with.
If BTC will have the hard fork, means BTC will sink.
Is that means that all exchanges will now put ETH as prime coin to trade with?
No no no. Even if there will be a split that wont never happen. There is too much big investors with BTC for that to happen.
It is just a fork and that doesn't mean the end of it.
The throne will still be with bitcoin and ETH will stay there.
Let us not make conclusions out of this.
Read theymos news for you to know how to secure your bitcoin. If that is the case then it will be back. Just secured not to end up losing your coins.