@dogletsrock - if it is easier for you look at trains to Chesterfield or Sheffield, I'm quite happy to come pick you up from either station and drive you out to Matlock to get sorted.
Do you have a spare car key in order to drive the car home?
Have you managed to contact the festival directly at all? I'm just wondering if your DH was taken ill and unable to tell the workers his son was still there whether they'd have a record of him (or even a John Doe) being sent to hospital or something.
Don't be scared of approaching your friends or family for help now either, it is an emergency situation and I'm sure that they would be willing to leave their kids with their dads/grandparents to drive you up here to Derbyshire.
I doubt you're going to get any rest worth a damn, is there anything practical you can be doing now like getting together food, RAC/AA membership copy, finding emergency car locksmith in Matlock if you don't have a spare, clothes, extra charging packs etc.
Could you look on traveline and see whether a coach to a nearby city and then direct train to Sheffield might be faster than a local train service and then messing round with a train to Matlock?