You can leave a dispatch-related conversation, however, until the task has cleared, the conversation will remain open and can be accessed through the Actions section from Tasks or from the Dispatch tab in Messages.
If needed, you can rejoin a conversation by accepting an invitation from a conversation participant.
To leave a conversation:
Tap Messages from the dashboard.
Open a conversation:
To select a dispatch-related conversation, tap the Dispatch tab, then tap the conversation you want to view; or
To select a conversation unrelated to a dispatch, tap the Messages tab, then tap the conversation you want to view.
Tap Details > Leave.