And it should also be remembered that Marvel studios are notoriously thrifty. If Spidey's right go up to the highest bidder, then, while we would all like to think that Marvel is the webslinger's natural home - but they could well be outbid by another studio.
Or they might regain the rights for nothing, depending on the exact nature of their contract with Sony. If the rights are "non-transferrable", then ONLY Sony would have the right to make Spider-Man under that contract. An end to Sony's entertainment division might see an automatic reversion of rights to Marvel.
I don't KNOW that's the case, but such a restrictive contract would be typical of Marvel.