He didn't own Pitmaston as far as I know, except for the brief time that Centrepoint Ltd possessed it before splitting and selling off the estate. Unless there are recent docs that say otherwise, after that he was no longer a named director of any of the companies who bought the lots.
I don't think his death will make any difference.
This site lists him as the director and/or secretary of up to 13 companies. Even if he turned out to be one of the hidden Pitmaston shareholders he was an experienced businessman and I don't doubt that there are contingency plans in place to look after his business affairs.