Uhm.
Depends on how the contract is written. They are accepting or refusing the contract, not cherry picking the unit whenever they like.
Of course, if the contract language is unenforceable....then it's a different kettle of fish.
If the contract isn't 'hinky,' I think the seller is entitled to the full payment, 2020 first use, and may exercise control of the 2019 use if it's paid for.
Of course, if the contract is exercised prior to payment of MF's etc.... then things could change.
Marriott will send a contract that specifies the terms of the ROFR. The seller is NOT required to sign the contract AFAIK.....if it doesn't match the terms of the original agreement substantially. Of course, time is of the essence, equivalent payment (no Mf's no 2019 use) could be valid under the ROFR terms. Who knows? I didn't read the ROFR page very well....I'll go look.
You know, I think the seller can decline sale and resubmit later (maybe Dec?), but at some point.....they will force the issue.
I'm not a lawyer and I have no idea what I'm talking about.....but you get the gist.