User blog comment:HunterxPhantom/Chrollo's Stolen Abilities/@comment-26871105-20160714162126

He seems to be able to return them, considering while technically he "stole" Shalnark and Kortopi's ability, it's more like a "borrow" as he'd asked whether or not Shalnark wanted his ability back while they were on the phone.

I think the logic behind is that "stolen items can be returned", not like Chrollo is a person who'd do that 99% of the time though (and the remaining 1% is because he gains more from having them returned than kept).

As for Light Nostrade's income and how he managed to survive the astronomical debt of 3 Billion Jenny, I guess you could thank Kurapika, who is also apperantly the world's #1 financial advisor on top of pretty much everything. We have absolutely no idea what Kurapika did though, I doubt Togashi has any idea as well.