You investigate and help, if possible. It's just being human. Not even because you ride a bike or anything, its just the right thing to do.
Couple of years ago, on my first GS, my son and I took the canal roads to Beestekraal. I overcooked one corner too, went down and tumbled a bit onto the embankment about a meter or 2 lower than the road, and the bike ended up teetering on the edge of the canal. Out of nowhere, seemingly, 4 locals popped up and helped us drag the bike up to the road again. And they were not even bikers.