It's absolutely one of the worsts day that is going to happen if you lost all your bitcoins. That's why I put it now on electrum where I have the seed, private keys and master public keys and I can recover my wallet any time. So for you people out there that is still not prepared before August 1. Make sure that you hold those keys.
I am sure that you wont loose you coins but you might loose the benefits of the split as usually you are supposed to get coin on a equal ratio of 1:1 if there is a split and if you save your coins in exchanges then you wont get those but that does not mean that your coins will vanish because the coin with the biggest followers will be the leader and that will be the coin you will be getting if you store your coins in an exchange.