Sorry to hear about your situation.
In general, I would start by saying that this sounds like a very complicated situation, so I would have to defer to your father's
doctors who undoubtedly know much more about the specifics.
That said, in cases where someone clearly needs a surgery, you often have to go ahead with the procedure even if there are risks. There is an elevated risk of stroke during a surgery, but every decision in life involves risks and benefits, and this is no different. I think you should have a sit-down discussion with all the involved physicians - including the Neurologist and Surgeon - and decide given all the risks and benefits, whether or not it would best to proceed. Simply giving a blanket statement of "surgery contraindicated due to stroke risk" is not good enough, the discussion has to be more involved.
Sorry I can't be of more help, but again, this sounds quite complex and requires input from all of father's physicians.