Depends what the failure is. If the important stuff is scattered around 20 different devs, one leaving is significantly less of a problem. I'd much rather piece together what someone was doing on one piece of work than have to try and piece together an entire 20 person project because the only one that knew how to drive the project left.
Also, if you own code and are responsible for it, part of that responsibliity should be making sure you have someone with just enough knowledge of the code to take it over should you leave. That's far more feasible if you own a small piece of it than if you own an entire code base.
Also, if you own code and are responsible for it, part of that responsibliity should be making sure you have someone with just enough knowledge of the code to take it over should you leave. That's far more feasible if you own a small piece of it than if you own an entire code base.