Right, if this is true (possible I guess, but does sound a bit Syndrome-from-The-Incredibles), even if there's really no technical way at all to terraform Mars it's hardly the end of the world, uh, planet.
Not least, terraforming would take centuries in any plausible effort. If he goes to Mars to die, he'll die in a pressurised environment whatever happens.
Being a billionaire makes pivoting to executing on new dreams easier.
Newfound empathy could give him a new dream of making that American Dream happen for others.