Morning dress tailor
My guess is he's mostly likely dead or at least retired.
That may be likely as no individual tailor would last that long, however, the firm of tailors is still in existence and trading on Savile Row. I know that when you buy a garment new from one of these firms alterations can be purchased for a good number of years if not the rest of your life. However, I do not know if they would find it rude that I would want to alter the garment as I am not the original owner.
Would situation be different if he had inherited it from a relative?
The tailor is Davis and Son, I think I will give them a call as HansderHund suggested. However, I do see that the form is not great as it could seem like I want their services on the cheap. I like to think that is not the case as my motivation here is to re-use a very beautiful and well designed morning coat which few tailors, given the complexity, can alter without ruining