crates.io requires a license field before you can publish. The code will still be bound by that license, unless the author ever changes said license.
It's not likely to happen. I went through that exact process once, but was deferred to the Crates.io policy, which I admittedly had forgotten to look at. The relevant section:
A more case-by-case policy would be very hard to get right, and would almost certainly result in bad mistakes and and regular controversies.
Instead, we are going to stick to a first-come, first-served system. If someone wants to take over a package, and the previous owner agrees, the existing maintainer can add them as an owner, and the new maintainer can remove them.