For the last month all I've been doing in the studio is quilting. Can't count how many spools of thread I've gone through and how many bobbins I've wound, but I can tell you with absolute certainty that it's a drag to run out of bobbin thread somewhere in the center of the quilt. But I have figured out a routine that minimizes the angst.
Here's how I do it.
When you realize the bobbin has run out, lift the presser foot and pull the quilt toward you till you find the last complete stitch. Pull the bobbin thread to the top of the quilt. It's probably only about a half-inch long, not long enough to bury with certainty that it will stay buried. So pull out a few stitches back, always pulling the bobbin thread to the top, until it's at least an inch long.
check out this tutorial.