he was the social glue of our department
It reminds me of an old work place. I worked for a small, family-operated business where the owners were hands on. One of the office staff left for a new job, the first key person to leave the company, and they treated her really badly. She was the social glue and well liked by other key people and - it was all downhill from there.
Companies always make it clear that people are replaceable, but they do not measure the impact that this will have on the production of the personnel.
It is clear that "social glue" is very important. And as much as we all want to be one, we can't because charisma and that peculiar personality is something we are born with.
Interesting how I never stopped to think about this. Thanks for highlighting it.