Earlier quoted context omitted.
Microsoft would never do that unless their hands were forced. Too much potential business with them. We could try forcing their hands by removing all our code from Github?
More effective would be those who are at orgs paying for Github Enterprise to express to their account managers they'll take their business elsewhere if Github is unable to defend it's platform from malicious actors. Github don't care if you take your code elsewhere. They most definitely care about revenue (and developer mindshare a somewhat close second).
So the sales rep is likely just going to be confused by the attempt to use unrelated leverage.