£5m. Maybe more.
Most commercial deals the club would have would reduce as a result of relegation. Solidarity payments from the PL reduce massively between the Championship and Football League too.
Gate receipts may be relatively stable, as...
1. Season ticket holders have to make the renew/don't renew decision quite early on, almost certainly before the club's fate is known.
2. Although far from guaranteed, obviously, the club would expect to be pushing for an immediate promotion and a winning team gets bums on seats.
Re STH, they don't really. How about saying 'no' in March, and then starting again in august if we stay up ? Can't imagine there will be a waiting list........