The hidden service builds a circuit just like a normal tor client does, passing through 3 different nodes to connect to it's introduction point.
It is nowhere explicitly mentioned in the tor protocols how comes that an introduction point can still contact the hidden service if time has elapsed since the service has chosen them, but I think it is implied here that the hidden service keeps it's connections to introduction points open.
That means also that if the service goes down temporarily, when going back up their tor client will reconnect to the introduction points and if it doesn't there shall be no way and no need for the IP to find the service back.