Even if there are no solid plans (certainly, there's no money!) for extending the line south of Larkspur, it makes sense to update your survey and property data regularly. Stuff happens, and adjacent owners/residents can cause problems if they encroach on your property and aren't found/dealt with in a timely fashion.

My guess, though, is that the highest and best use of most of the line south of Larkspur is in fact a bike path. Given the restricted space at Larkspur, I could see going a bit farther south if money fell from the sky to find space for a more comfortable and bus-accessible terminal/service area, but the cost of replacing the bridge(s) would be astronomical so I wouldn't expect it in most of our lifetimes.