This is such a sad posting.

I do think it's more likely he's approaching retirement than death tho, he may be planning not to retire also. Maybe working is what's keeping him young.

I think it would be a good idea like someone suggested to be up front in your concerns. Because for as long as you consider him your main T, you'll never connect in the same way to any other T and the loss, if it is coming would be made harder by the fact that you lost him not only as a person but you lost your main therapist. Maybe it would be better for you to forge a relationship with another T and allow that to deepen.