This is not an absolute demand that Republican Senators oust McConnell no matter what. If no preferable alternative emerges, he'll give them a pass. But it puts the squeeze on incumbent Republicans, and GOP candidates challenging Democratic incumbents, to withhold support from McConnell, or reject him outright.
In practical terms, this probably doesn't mean all that much for McConnell, or the rest of the GOP. Most Republican-held seats aren't in cycle this election, and many of the Democratic seats that are in cycle aren't in play.