The global lock is a feature of MRI that basically wraps a big mutex around all of your code. That's right, even if you're using multiple threads on a multi-core CPU, if your code is running on MRI it will not run in parallel.

You don't need to be in person, and many people would surprised how effective teams can be even when they're not in the same room. All it takes is good communication, and by that I mean: 1- good communication technology, like a good net connection and good chat software and good cameras, 2- good use of technology for communication (IM software is not sufficient), and 3- good communication practices (which amounts to: communicate early, communicate often).

Yes, one who knows how to communicate. But you wouldn't want an on-site employee who doesn't communicate, either.

So are on-site employees, who can screw off just as much as an off-site one.

if the remote employees are not providing enough value to justify that investment in remote workers

Then fire them. This kind of draconian move won't get Yahoo anything but an even bigger talent hemorrhage than it already has.