We routinely see red lights at the end of the runway on takeoff. Late in the takeoff, I'm not sure that I want to be attempting to get stopped while looking at the red lights. whatever lays beyond them isn't in my favor, though returning to land with the full runway ahead of me certainly is.
Can I fly it around and get it landed by myself? Without question. There's no question I'd much rather do that, than attempt to do a high speed rejected takeoff.
The original question involves an incapacitation at 80 or 100 knots. We generally brief such that any problem up to 80 knots merits the rejected takeoff. After that, it's controllability issues or clear safety of flight issues; the other pilot incapacitated isn't one we brief, or one I'd consider necessarily significant enough to perform a high speed reject. Does the other pilot being unavailable preclude the airplane getting into the air or affect directional control? No. We're probably going flying.
When asking if the takeoff should be rejected at that point for an incapacitated pilot, one may be asking the wrong question. Perhaps a better question is who is going to take the airplane into the air. If the other pilot is truly incapacitated, then clearly the takeoff (and subsequent return for landing) will be performed by the one who isn't incapacitated. However, if it's a matter of a full-functioning pilot who didn't hear the challenge, or wasn't heard (I've had ICS failure at that inopportune time...we were both talking, yelling even, but couldn't hear each other over the increadibly loud radial engines)...book says if no response the second time, take control. Nobody was incapacitated. Just deaf.
High speed rejected takeoffs present a multitude of hazards, often far less than continuing the takeoff.
Simply because the performance data says the airplane can be stopped aproaching V1 doesn't mean that one should without just cause; an aircraft under control and accelerating properly is not necessarily just cause to reject the takeoff.