I bet they have to arrange some sort of sound deafening structure between the depot and the new development, although the buses exit from the opposite end (of the proposed development). However they come back in to the depot after midnight sometimes and will be bordering the edge of this development. Apparently sound tests have been done however which state there should not be a problem.
I recently had to visit Barnsley depot for a training course. The depot has been there for quite a while. Subsequently some new houses were built opposite the main exit to the depot. Due to complaints from the new residents (although the depot has been there for much longer,and people bought these houses knowing it was there), Stagecoach have had to plant new trees to obscure its view, buses cannot exit the depot with headlights on (even in the dark) until they are on the main road because their lights will shine in to the houses, and they have had to pay for triple glazing for some properties to keep the noise out!!
Bearing this in mind, I would not be surprised if Stagecoach relocate to Markham Vale. I know Sir Brian Souter has been a couple of times recently- maybe thinking of making Stagecoach land available too - who knows?
It would be a shame because Stagecoach depot (although old) is self containing, in other words it has engineering bays, paint shop, upholstery(bus seats), electrical section, full self contained MOT facilities,canteen etc.
At least the buses are undercover in winter(at Chesterfield) unlike at Barnsley. They are parked in the open air - so get frosted up in winter.