Where I work the same situation often comes up -- a developer may spend weeks doing research for a specialized function building prototypes, etc.<p>Ensure the specialized developer is doing due-diligence in defining and verifying the module works as intended and have others analyze its interactions in the larger system to prevent cascading failure, conforms to application norms, __is documented__, etc. Even if most others wouldn&#x27;t understand the internals during review you will be taking steps to keep the risk localized. If the bus arrives and you lose the specialized developer then it&#x27;s reasonable to assume another developer would need to spend nearly as much time to catch up on the research.<p>Otherwise you&#x27;re responsible for making the decision to invest more developer time now in understanding the problem&#x2F;implementation vs. later - a gamble at how much time until that developer leaves.<p>Taking over specialized&#x2F;legacy code is part of the job. It can be painful but there are steps you can take to minimize that pain later.