10-19 they would never have got rid of space - and arguably other potential tenants would have paid them to relinquish their rights

Exactly that. They could have easily found another renter/sublet it for no money lost (potentially even gained) those days.

Yep, one company I work with closely made something like $16M through subleasing or leaseback (I forget the exact arrangement) in early 2019 after they decided to reduce their office footprint.