What if said employee pulls in 10x, 100x more revenue/value than average worker for the company? Would you fire him because the rule book say so? That said I trust in effective communication as soon as possible to manage difficult situations or misbehaviour. Often the reasons can be deeply personal or family related and people are preoccupied with stuff outside work. We are human and human relations are variable, not absolute.
Bob Sutton's "The No Asshole Rule" calls this TCA - total cost of assholes. TCA incorporates the cost to replace people who leave because of the asshole, time spent by manager calming people down and cleanup, customer relastionship issues, etc.
10x, 100x revenue is only one piece of the story.
Great performance does not require being an asshat. It's (nearly?) always possible to find an equivalent performer who's pleasant to be around and a constructive team member.
Unless you're pulling in that revenue directly, because you're in sales or negotiating deals with other companies, it's impossible to make the claim that someone is 10x more valuable to the company.
Of the most highly productive devs I've ever known, most of them are not 10x more valuable, they are just more productive. The very few real super-programmers I've ever seen (maybe 3 of them in 20 years) have skyrocketed into the stratosphere, make lots of money and lead large teams. So, I don't think anyone super valuable would get fired, but my experience is that they get moved (up).
Most highly productive devs I've known are productive people that are prolific and also do a proportional amount of damage. I've known several people in different companies that were smart, prolific and very opinionated, and they would inflict their ideas on everyone and get support from management and not enough pushback from other devs. They implemented processes that were needlessly complex and caused measurable drain on the productivity of everyone else. You can lose your 10x productivity benefit really fast if you suck 10% from everyone else.
One guy I knew was a 10x performer and lead a team, but had a nasty attitude and took down the morale of everyone he talked to regularly. Even though he performed, he was causing everyone around him to go slower and work less. To the parent comment's point, this guy's productivity kept him from getting fired despite his misbehavior.