Don't think the board would think it would be a disaster only relegation from L2 would be that.
Wenger has stayed too long and all good things come to an end and time he moved on.
SD must be given time but is not helping himself with the constant chopping and changing of the team. We do need some decent Strikers but doesn't every team? If we stay in the bottom 4 then its a toss up whether to get more loans in or to try and give the kids an extended run. eg Resting Walters is understandable but maybe counter productive to his form and confidence as it is to any player who has played well and then dropped the next game.
He has shown he can do it when he took over from Dario and lets hope he can again. I think if we did get relegated and then go into the bottom six like Tranmere and Carlisle have, then the case for a change would be unchallengeable. The board would act then as they did before. But that is perhaps being too pessimistic and lets hope it all comes together.