There was much panic and thinking it would all go horribly wrong, and indeed it was madness for the first week. Then the people who took over started to stabilise some of the worst parts of the system and it all sort of fell into place after that.

Fast forward a couple of months, the project was pretty much hands off and we all realised that keeping a whole team on that project had pretty much been a giant waste of money. They did nothing but create fires for themselves to fix. The Team B's exodus was actually a really great thing for the company.

I suppose the thing to learn here is, that you need redundancy in your teams. If we hadn't had other devs to step in and take over, it would have been a bit different. Still, I'm not convinced that a handful of contractors couldn't have been brought in to the same result, just more expensive.

Both kinds of teams are needed. Or even better, teams should not be divided like this, everyone should do their shares of both breaking things, and creating value and cleaning the mess and scaling the things.