There will be some die off but not completely, That may start a cycle though which isn't at all what you want during QT. The Cheato will also not survive, it may survive maybe 2 or 3 weeks. Your best bet is to do a separate tank. Most people don't want to do a separate tank because they don't want to break down the main. If you are already taking out the rock and sand, you may as well take out the fish instead, That way you keep the sand and rock in place in the main tank, and the QT can be set to go in a matter of a few weeks. Which may not be what you wanted to hear, but taking out the source of bacteria is the same as starting out with very little bacteria. You can seed it with a sponge or some filter media from the sump. A QT doesn't even have to be a tank. It can be anything at all that can hold water and big enough to house all of your fish.