The fact that he BOTH (1) wants to decline advice not to go AND ALSO (2) wants to decline accommodations once on the ship, is telling. The presence of BOTH issues argues that this is a decision born of a psychological desire to convince himself that what has happened has not happened, and that what he is afraid of being true is not true. As a psychological defense mechanism, his position is understandable. But, understandable or not, his position argues that he is not truly wanting an honest assessment of what to do here. Instead, his position is about an emotional reaction to having had a stroke.
If he is to go, it should be with maximal use of whatever accommodations as may be able to help -- the most that can be offered, not the least -- and only if, subject to those accommodations, his physicians agree.
BTW, I am a neurologist