I have answered all your questions as below :-
1. How did this happen?
Zend is pretty crucial, and it was working previously. Whatever change was made that broke it, should have been tested on a development server before being deployed to a live server with customer
website hostings on it. You guys do that, right?
Ans :- Not sure why Zend was not running on your server. We dont do any experiments on live servers.
2. Why did it take over a week to resolve?
Ans :- One of our windows server crashed and last 3 - 4 days have been a nightmare. Our response time for support tickets had an impact due to this problem.
3. Why has nobody responded to us?
Ans :- One of our system admins tried to make it work on the day you had opened the ticket but he was not successful with it. Next day we were hit by crash of our other windows server.