That's kinda the funny thing with Omega, and act IV in general... If you can make it as far as beating Tau, you're probably on a roll. And there's really not much reason to ever retreat early, since you earn enough skulls there that you actually lose more of them by *not* spending them to save all your stuff.
Curious tip for Omega though: His stat-deleting attack needs the stat to exist in order to target it, but there doesn't appear to be any weighting based on the value of that stat. So taking along some camp items that provide like +1 HP per day or +1 Retaliation damage, or some other stat you won't have on your character, means you'll have an entire new stat category that will have the same chance of being wiped out as, say, Max Skeletons. Or Damage.
If you need some more specific tips... As ever, deserts+oases is king. His fight is generally an endurance match anyways, so the fighter's passive really shines if you give it the chance to do so. His standard attacks can also be dodged like any other. If you wanna get fancy: Omega has some pretty massive physical armor, so if you can squeeze 2-3 storm temples in line with the campfire, he'll go down like a chump (legitimately the fastest kills I've ever had).