The 'it' refers to the case, the investigation. The FBI pulled rank and took the case away from them. Now it is out of Brad and Warden's jurisdiction. As Warden says, they have been pulled off the pursuit (case, investigation).
To answer the question, these two can no longer work the case, meaning they can't pursue the criminal or continue the investigation.
There's three issues here, complex sentence structure, a use of ornate, Biblically inspired language, and some playful, allusive indirection, all of which are distinctively typical of the educated Southern American mode of speaking and writing. It also helps to know that John Wesley was the founder of Methodism, a Christian Protestant denomination founded in England, but influential in America.
Mindful of John Wesley’s strictures on the use of many words in buying and selling, Simon made a pile practicing medicine...
Simon --being consciously aware of John Wesley's prohibition on talking too much while conducting business dealings --became rich practicing medicine instead...
The joke here is that Simon interpreted narrowly a statement of John Wesley's that was probably meant as general advice against being too concerned with the pursuit of money.
...but in this pursuit he was unhappy lest he be tempted into doing what he knew was not for the glory of God, as the putting on of gold and costly apparel.
...but he wasn't happy being a rich doctor, because it tempted him to become worldly and extravagant.
This second part of the sentence isn't as hard to parse, but it makes some allusions. "Gold and costly apparel" is a quote from a John Wesley sermon, which in turn alludes to a passage from 1 Timothy 2:9 (The Bible, New Testament) that warns against taking too much pride in your clothing and appearance.
Best Answer
A gig in this context just means "a bit of work"
(Macmillan Dictionary)
And so a "side gig" is a bit of work "on the side", meaning "outside your normal employment".
So, it's saying that some of the people were in the Yahoo office, ostensibly working for Yahoo but in fact doing paid work for other clients.