What are my chances to get into FMS Delhi or older IIMs? I have 94% in 10th and 78% in 12th in the Maharashtra board.

Your chances to get into FMS Delhi and any other older IIMs depend upon three criteria.

1. First is how your CAT exam went. If you are in a general category, then you have to score at least 98 percentile in the CAT exam to get a call from these institutes. 
2. Second is how well you gave the interview. An interview is a make-or-break thing to enter into these institutes. If you give a good interview, then the interviewer will consider you even if you are lagging behind in a few aspects. 
3. Third, is the student profile, like your 10th, 12th, undergraduate percentage, and work experience. 

The major contributor to your admission would be the first two factors. Your profile does not make such a difference when you excel in the first two. You could get into one of these prestigious institutes if you work hard enough.