What does 'alumni status will be provided for IIM Rohtak' mean? What are its benefits like IIMB alumni get to keep their email and enter the campus anytime?

The alumni status means that you have graduated from IIM Rohtak. The benefits of having the alumni status of IIM Rohtak include having an official email from the institute. This will be your personal id and you will have lifetime access to it. As an IIM Rohtak alumni, you will be invited to the alumni reunions. 

You can use your alumni status to network and receive better job opportunities, as well.