Howdy, that's almost me! AMA!
I've spent 10 years as the lone dev at a small medical facility, writing database software and dealing with lab hardware etc.
I guess I've touched 100% of the codebase because I wrote it all, but I always wonder if my skillset is so niche that I'll always be at small companies.
Here's the deal though, work isn't everything and I'm at a job that recognises that.