The only reason the 10+ authors (all plenty skilled in Haskell either before joining or due to working on the project) were all gone is because said senior came in and pushed them out. As I said, the team was fully functional, in production, low bug rate, generally happy.
Is it really cheaper to rewrite an entire working system (that took a year+ to build in the first place) than to just learn something new? I have learned a new language in order to inherit a working, hardened, well-made system before. But I am finding for certain senior engineers, the answer to "can I learn a new language" is a resounding no. The cost is infinite, so of course it's cheaper to rewrite. Plus they are incentivized to rewrite thanks to political reasons (i.e. it's a great way to get promoted).
The last time it happened, I was lucky enough to be accidentally shielded from accountability due to the organizational quagmire that resulted from the team blowing up. I basically got to do nothing for a year and make $200k. And I got to be less than useful to the principal who made the powerplay (not -10x level but I did get to spend time maintaining the existing FP system due to it having a single production consumer left). That dude did not like that I never turned my camera on. My manager also seemed pretty checked-out, so that was extra buffer.
So to summarize, I'll say that it's easy to have be prescient when you make self-fulfilling prophecies. That's one skill I've learned from senior management over the years.