No, there is no way to add a new device is place of an old device but the bigger question is why is the device "dropping off" in the first place. If it is just a question of signal strength, you may need another repeater. But you shouldn't have to remove and rejoin the device to the mesh in order to fix that.
That could very well be. If for some reason when the power is restored it's also causing the device to factory reset itself, then it could very well have to be rejoined to the hub and it would get a new "spot" in the database, since it is Z-wave and not Zigbee. Z-wave devices get a unique ID assigned when they join to the hub. Zigbee devices determine their unique ID and tell the hub "who" they are. That's why you can re-join a zigbee device that has been reset without replacing it in all apps. Z-wave doesn't work that way. I don't know enough about the Radio thermostat to know if that is possible but if it happens when you lose power, that could be the reason. Sorry I couldn't be more help.