Question
How can you tell if a drosera hibernaculum is healthy?  I'm not sure if this plant I have is going to come back, or if the hibernaculum is rotten.  When should I look for growth in the spring?  The plant is a filiformis/filiformis.

Answer
Given your location in California, I would expect your plant to have emerged from dormancy by now (unless you're in the mountains closer to Nevada).  Despite some of the snow and hail we've experienced at our nursery this past week, our dewthreads are showing new growth.  

To check on its health, carefully peel back the out brown layer over the hibernaculum.  Keep peeling it off until you get to green tissue.  If you don't see any green tissue, the plant likely died during dormancy.

There are many reasons why a plant doesn't make it through winter.  With dewthreads, it's often due to fungus, but other factors could affect too.

Good growing!
Jacob Farin