Hollins sums up the position well, although I think this is stretching a point:
There are plenty of retail outlets outside it [the town centre boundary] anyway.
Actually, a close look at the map suggests that there is not a single shop outside the red line, apart from those which are not in the centre at all, such as Marple Bridge, Rose Hill and Hawk Green.
A supermarket at Dooley Lane can almost be ruled out, because it is so far 'out of town' and therefore completely contrary to planning guidance. However, if Hibbert Lane is sold for housing, and therefore no longer available for retail use, then it's possible that Goyt Mill could come in to the frame as a supermarket site by virtue of passing the sequential test.
It would be ironic if the gang that stymied the college's development plans (MIA, MBF, councillors, MP) found that their actions had led to a supermarket being built further away from the town centre, and therefore, as hollins points out, potentially more detrimental to local shops than a Hibbert Lane Asda would have been.