First off- how big is this lake? Are we talking Lake Superior, Lake Hartwell, or Lake Wannabebigger?
What are the conditions on this lake? Does it develop waves of good size, have sandy shores or cliffs or seawalls, etc...?

I've done the vast majority of my sailing on the Gulf of Mexico, Tampa Bay, and the intracoastal waterways. Most of the time, I was sailing solo in the company of other single-handers- we were all on 18' boats.

If one of us went over, we'd sail up to them and tie 30-40' of anchor line from the bow of our boat to the stern of theirs. Furl the jib, center the main but leave it a bit loose, pull the rudders up and let our boat drift down (which also helps pull their bows into the wind and keep them there). Then hop off and swim upwind to the capsized boat that is drifting towards you- use the line tied between them if you want. After getting the capsized boat back on its hulls, pull your boat up and hop aboard, untie the anchor line, unfurl the jib, and get going again.

I haven't had to do this in "survival conditions", and wouldn't want to. The boat that's drifting downwind on the end of the line can sail around a surprising amount. Occasionally I'll anchor or tie off the a piling with the jib furled and rudders up, main centered but not tight, and find the boat sailing over its anchor or past the piling.