H1b to F1 by travelling

[HRN]

Hi All,

Currenly I'm in US on H1b visa & recently I got an admit from one University for MBA. Now I'm planning to join the course by July/August.
Now converting my H1 to F1, I came to know that I can do it from US (COS) or I can go back to India and get it stamped.
Since I might need to go back to India during my course - I'm planning to go back to India and get it stamped , So I wont have any travel constraints.
Now, if my F1 gets rejected - I want to know what will happen to my existing H1 visa.
Please do let me know.

Thanks in advance.

Regards,
HRN