Well, you walk. 马死落地行. The Chinese proverb is meant to describe that people can always find a way. It may not be as great or as efficient, but you can still reach the destination.
And that's the lesson I learned from watching my teammates in Outward Bound. To me, it wasn't that challenging physically. Don't get me wrong, the kayaking is still exhausting... it's just not extreme exhaust, like I've experienced hiking in Tibet or towards the end of the Green Power 50km hike. Anyway, even though some of my teammates claimed to be unable to continue, after a little rest, they can still re-engage. Whatever the so called limits are, you can always break them and establish another limit.