Pretty much the only thing you could offer him would be the chance to save his baby. He started the company, he built it up, and now he could (in theory) save it. It's a legacy thing.
Bill Gates's legacy is pretty secure, and obviously he's not hurting for cash. And it seems as if he's in a more humanitarian mission at this stage in his life. But if there were anything that could lure him back, my guess is that it would be the goal of keeping Microsoft relevant -- making it into a 100+ year company.
I read it more like they'd go to Bill Gates saying "We think you're the best man for this job, all these people agree, will you take the reins for a year" and if he accepted it'd be because he cares about MS, etc.
Bill Gates's legacy is pretty secure, and obviously he's not hurting for cash. And it seems as if he's in a more humanitarian mission at this stage in his life. But if there were anything that could lure him back, my guess is that it would be the goal of keeping Microsoft relevant -- making it into a 100+ year company.