Another thing to consider is will Thameslink actually cease the shuttle bus operation as it is part of their franchise agreement with government? Will they run a cheaper bus service so cutting demand for the Dart, as the scheduled travel time is only one minute slower but actually stops outside the terminal rather than a two minute walk away.
The rail franchising model is now dead. Rail operators will enter in to agreements with HMG to run its railways for a fee, and HMG will own the fares. That will (presumably) be the opportunity to amend the Thameslink operating agreement.