The ‘Alumni status will be provided for IIM Rohtak’ basically means that you will be considered a legitimate student of that institute. So you were not an external student but a credible student and will be given equal treatment as any other graduate of IIM Rohtak. 

The reason that it is specifically mentioned is that students who have done a certification course/workshop for a week are not granted alumni status and are considered external students. It is only applicable to graduation equivalent courses.

Assuming that you are referring to the Post Graduate Programme In Management For Executives(EPGPx) by IIM Rohtak, here are a few benefits that students with alumni status can avail.

• IIM Alumni Tag: You associate yourself with the IIM tag for the rest of your life and continue to avail the benefits that come along with it.
• Official IIM Email ID: You will be receiving the official email ID from IIM Rohtak. This will be like your personal id which you can use forever.
• Invitation to Alumni Reunion: You will be invited to Alumni Reunions occasionally wherein you can build a solid network. Strong connections can help you climb the corporate ladder quickly.
• Job Opportunities: Your job opportunities will increase manifold owing to this IIM Alumni tag. A lot of companies ask for IIT/IIM Tag for strategy and other business-oriented roles while recruiting. 

This, a person with alumni status at IIM Rohtak is given due importance and continues to reap benefits from the Institute even after leaving it.