If the skill difference among your devs is really high, it may be preferable to have the best programmer leave, or at least change roles (architect, team lead, trainer), as this may increase productivity of the median workers. At least the skill difference should be treated as a risk and properly mitigated.
In the role in my sibling comment, I somewhat filled the role of the developer that went away. Hardcore Java/Spring Boot guy who could wrap his head around these amazingly complex code bases he made that the younger/less experienced devs could not manage on their own. I spent a ton of time mentoring in my role, and hopefully helped undo some of the mental damage the previous guy did :D. Things were running much smoother when I left then they did when I first joined at least, with teams that could have chosen whatever language they wanted choosing Go voluntarily.
