No. No part of the plant will stay beautiful while rest dries up. For sure, the plant will die off above ground but the ambient temperature in the soil will fry the root system.
It is in astilbe genes to sprout in the spring, flower, die back, rest during the cold winter and start all over. It is NOT in their genes to hide out in the soil waiting for it to go below 70 degrees so they might spring up out of the ground and flower. The HEAT is the HEAT, is the HEAT. You can't change it. You have to grow things that love the heat.
