Ryanair cannot go anywhere else in the LON area with such scale.
Any potential buyer will have to swallow this, if they demand 'normal' charges then RYR will start cutting routes to move airframes across Europe or base them in Europe and run the routes back to STN.
Either way unless the new owner has to have deep pockets, they are not going to attract new business whilst RYR are dominating.
An aggressive Gatwick and Luton and Southend hungry for more business, it's going to need a revolutionary business plan to move things forward for STN.