According to PWInsider.com The Undertaker will be returning on the 2/24 episode of Monday Night Raw. Their report says his return is confirmed and the date was locked in sometime in past 2 days.
The reason why WWE chose this date is to hype up the launch of the WWE Network. This has caused speculation that we could see more big name stars on the 2/24 edition of Raw to build up even more hype for the launch of the network.