re: Has the SEC ever permanently dismissed an official for poor performance?

Never has happened and likely never will. It woudl take something egregious like proven gambling interests to cause an official to be dismissed.

You've got to understand that college officials are not NFL officials. They're not full time with a salary like NFL officials. They get paid part time for a few weeks out of the year. Most of them are business owners and lawyers and shite like that during the week. The way the SEC sees it is like any other employer would an employee: if they're not doing anything way out of line, why fire someone who is not only already trained and experienced in that line of work but also is willing to put their face and name out there for entire fanbases to vehemently despise (given the way some Bama fans react to losses, this would be a deal breaker for me).

Is it fair and free of bias? Hell no. But until the SEC becomes the first conference in college football to hire full time officials, that's how it's going to be because it's cheap and easy and nobody is going to do anything more than piss and moan in response.