Please let SoM characters transfer to TBC/WoTLK there's no reason not to

[Asma-bloodsail-buccaneers]

They did make it clear what would happen

@Kaivax

Looking Forward

Finally, many Classic players have asked what will happen at the end of the Season of Mastery, and here’s the answer. When Season of Mastery concludes, you’ll have the option to permanently transfer your character to an existing Classic Era realm in your region. This free service will become available for a limited time at the conclusion of the season.
While we don’t yet know the exact destination realm and specific dates, you’ll have plenty of time to move your character to a safe home before all Season of Mastery realms are permanently closed.

Sorry you missed it.