Would this be in response to a question such as "so how is he?" without context it seems strange in English
Yes. Also could be an answer to "How are you?/Hogy vagy?"
"Sajnos nincs jól" is also accepted.
Could someone elaborate about the two variants? please
So unlike in English, no comma is required here?
No, in this case is no comma required.
Can Sajnos also mean "Sadly"??
Can you replace jol with jo? Or does the grammar conflict?
No, you can't. Because 'jól' is an adverb, but 'jó' is a verb. So it would mean '... I'm not good.'
I believe jó is an adjective (good) whereas jól is an adverb (well).
Does this mean the exact same thing as "Unfortunately he is not well"?