Are you saying that the food has been in a cold oven for an hour? Of course it will be fine. Just turn the oven on now. Put the chicken in the fridge and the rest covered on the side until the oven heats up.
I'd turn oven back on, cook for recommended time (not including the time oven was off). Joint it when time up. If it looks a bit pink, finish under the grill. Ditto potatoes - cut in half, if a bit hard, also stick under grill. It's what we did when the oven broke on Xmas day when we had a separate grill. Veg should be fine but can finish on the hob if you wanted to.
Do you mean you turned the oven off? Hmmm I’m a bit dubious about a whole chicken if it’s been sat in a warm oven for an hour cooling down the whole time. I also can’t work out what veg you were doing that was going to take the same time but I think the potatoes and veg should be salvable.