It may be assumed that they weren't fit for the battle, as Darius had his army stand to for a day as soon as he was aware of Alexander's approach. Arrian, whose numbers can be quite fantastic by the way, says, "In front of Darius's royal squadron of cavalry stood the elephants and fifty chariots." Another bit of evidence to suggest they did not take any part in the battle is, again from Arrian, when he details the flight of the Persian army and describes how the Macedonians "seized the Persian camp with their baggage, elephants, and camels."
Curtius Rufus, Diodorus and Plutarch don't mention elephants at all in their commentary on Guagamela.
So, I wouldn't allow any elephants in a Guagamela rematch.