The date of the Federal election is set by law. Congress would have to convene and change the law, and it still cannot be later than the first Wednesday of December, when the Constitution requires the electors for the Electoral College to meet.
Otherwise, what you say is correct, and it would not surprise me in the least if Congress called an emergency session and the Republicans would capitulate, because that is what the Republicans always do. But honestly, it was meant more as a dig on the Republicans in Congress than it was meant as an honest guess at what they would do. Yet at the same token, it wouldn't surprise me in the least if it went down just like that.