What kind of consultant jumps into a completely new codebase of a massive distributed system with hundreds of millions of users that has broken down to the point of being unusable and manages to fix anything, and how long does that take?
Sometimes it takes months for regular new employees to do anything productive in some of these codebases.
The underlying tech is probably standard (e.g. they probably haven't invented their own routing protocol), but the control plane is likely custom. The impact of making manual changes or changing the control plane is probably unknown, ranging from being fine to borking the system in some way that even reverting the changes won't fix.
The best option would be to try to rehire the former employees, probably at dramatically increased pay. I don't even know if that would work, though. Bridges have been burned.
Which is most probably why most of them were just kicked out. Twitter isn't complicated, it's literally just a micro-blogging platform.