Yep, a dementia sufferer could simply forget they have no medical and go flying in their own airplane even with mandated medicals. If you were to tighten medical requirements because of the extremely rare events of non compliance, then you end up like speed limits. That is, a stretch of road has several high speed accidents where cars traveling in excess of 200kph crash and cause deaths, so the limit is reduced from 100kph to 80kph. Will that have any effect on the road toll, no, because if the rate of excessive speeders remains the same on that stretch there will still be accidents. Or totally unrelated the excessive speeders may have already killed themselves so a reduction of deaths occurs on that stretch with no relation to the limit.