Update: Got a phone call earlier today.
He had a meeting with a couple of doctors (specialists) and they are not entirely convinced that mantle cell lymphoma is present. The other disorder (chronic lymphocyte leukemia) is most likely there, though. They did some tests (blood) and have some more testing to do over the coming months, but as far as treatment, nothing at this time. So, I guess, cautious optimism is what I got out of that phone call. He still feels ok, i.e. no symptoms.
We/I have received emotional support from wider family, people I have not seen in decades, from coworkers, people of all faiths and denominations, and of course the many kind people here at Bladeforums. Please keep my family in your thoughts and prayers.
I sincerely thank each and every one of you.