I'm sorry for your loss. I've never had anything like that happen, but I can imagine how devastated you and your family must be. Even so, you can't let it weigh on you too much, it won't do any good and will just drive you into depression. Sign or not, you and your family should assess the situation, and decide realistically what your next move is going to be. Most importantly, don't get discouraged.
But even if you had gotten to work sooner, I doubt it would have made much difference. Older structures (depending on how they were built) tend to burn very quickly. It happened to a restaurant near here, and even though the fire station was only a few blocks away, the place had nearly burned to the ground by the time they got there. Just be glad no one was hurt, and set your sights on making your new place even better. It sounds like you had a good customer base anyway, so you should have no trouble getting people in the door of a new building.
Good luck to you, whatever decision you make.