[conor-]

Wouldn't the large amount of existing services written in Hack be reason enough to keep it around?

The cost of rewrites at that scale certainly has to be far more expensive than the cost of paying a team to maintain HHVM

[throwaway2016a]

Generally yes but the languages are similar enough that the refactoring could be automated. Of course, that would create a fair amount of QA and testing work but if you have good test coverage you can mitigate that.