The “Don't Be a Dick” Code of Conduct
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It's interesting how we adapt our sense of normal based on consensus even within the smallest of groups. If you have a team of 5, and 2 are replaced, the dynamic for the remaining 3 changes based not only on how they individually interact with the new people but also with how the incumbents as a whole interact with the new people.
If A,B,C interact with D,E. Then A's relationship with D also depends on the interactions between BD, BE, CD, and CE
Whilst it's less obviously impactful, I think it's important to note that it doesn't have to be a whole person-swap though. Group dynamics can change over time as the people in it have different life-events, hit different points in their career-path etc. That change can then go and have exactly the same kind of effect that you outline, without any people-swaps.