Just had a chat with the son of the lady in my post, ladywoman. I was mistaken. They found the will before she died, not after as I thought, but she was going into a home...dementia.
They had POA and were able to phone around the solicitors using that to find the will she'd made but was now unaware of.
In my husbands case when his solicitor closed they wrote to him for permission to have his will stored at another firm. I guess it's too late for anyone to know if that happened in your case.
Good luck.