I'm not sure how a merger of Thomas Cook Airlines and TUI Airways would have relevance on high street shops. It would only become relevant if there was a merger of the tour operation, which looks highly unlikely.
Thomas Cook is likely to become a specialist hotel operator (Casa Cook etc), with its own tour operation. Fosun is said to be interested in buying this - they already own Club Med who operated on a similar model. It isn't dependant on an airline for its tour operation, and neither would Thomas Cook.