I look at it the other way around. They're probably talented enough to make it past probation, so their leaving was them deciding to leave, rather than not maki

I look at it the other way around. They're probably talented enough to make it past probation, so their leaving was them deciding to leave, rather than not making it. That is, any investment you make in them, giving them slack to get up to speed in a codebase, you'll lose because they don't stick around.