We would want re-opened tickets to go to the board they were last present on, which matches the behavior of the email connector.

Just a suggestion if this makes it onto the roadmap - this could be resolved relatively quickly w/ a checkbox in Messenger settings under Reopen Service Status to 'Inherit Re-Open Status from Email Connector', then query the ticket's current board by ID at service/boards/{boardId} and read the emailConnectorReopenStatus property to determine the ID to re-open under. This is what our network monitoring integration does at the moment (without the flag of course since this is always our preferred behavior)