Gelo of Syracuse as leader of anti-Persian alliance?

Prior to Xerxes' invasion of Greece, the Athenians tried to get Gelo of Syracuse to contribute a contingent for the upcoming war. He is said to have offered 28,000 men and 200 ships, but only on the condition that he be given command of either the Greek army or navy. So, three questions for those with an interest in the period:

1. What circumstances might compel the Athenians to take Gelon up on his offer?

2. How well would the Greeks do under Gelon's leadership?

3. What might be some of the long-term effects of Syracusan participation in the Greco-Persian war, presuming it isn't a total disaster for the Greeks?

Bonus question: how might this play into relations with Carthage, given the ongoing conflicts in Sicily?

Well if Gelo is in Greece with 28,000 soldiers it means they aren't at the Battle of Himera. I've read before that if the Carthaginians had won at Himera they would have been able to conquer all of Sicily so potentially this could lead to a completely Carthaginian Sicily.

I would imagine that Carthage would have a huge advantage in Sicily, and might be able to conquer Syracuse as mentioned above. Part of me thinks Gelon gave that offer knowing it probably wouldn't be accepted.

That's definitely a possibility. So maybe one of the requirements for this scenario is that there be a lull in the Greco-Punic Wars. Maybe if Terillius of Himera is not deposed or is killed by Theron instead of escaping and seeking Carthaginian support to regain power, then the Syracusans will be free to intervene back east?