my new guinia impatens cannot be brought in there are too many and already in the ground, so how long before I can but back the dead or appears to be dead staulks?

Cut back to growing stems as the frosted stems could become diseased. In future years you need to wait until frost danger is passed to plant out or protect with fleece if you have planted out and the weather turns cold again. Timing will depend on where you live in the States. Where we live in Scotland would not advise planting out of Impatens for another month at least.