indeed this is a very tough situation and I agree you may be able to stomach a conversation. I would say that this man is as you say, dying and you could simply call to show compassion but I'd say be prepared to just leave it at that, keep it short, show that you remember him and then end it. Once it starts veering to a point of anything to do with him trying to get some "information" out of you or seems like that's his goal, kindly cut off the conversation - using any means you can. or simply say you have things to do and sorry to cut it short... hang up.

It clears your conscience, serves to let a dying man know that people are still there, if that's what he truly needs. I am sure, knowing you that this will probably bounce around in your head and your conscience for awhile so I would probably lean toward suggesting you just get it over with but not without being prepared.

Hope this helps.