I can't see TUI ever replacing the Thomson brand. Lets face it since the merger with First Choice they have moved their world HQ to Crawley. TUI Travel plc were formed by the merger of TUI AG's tourism group and First Choice plc.
So most of the top executives are former First Choice & Thomson executives and will reckonise the importance of the Thomson branding. Just a shame that there is noone who would bring back the Britannia name back!