Engineering

There are many good colleges for B.Tech in India like IIT's, NIT's, IIIT's, BIT's, and many some good private colleges. I am sending you an authentic link from where you can SEE the best colleges for B.Tech in India according to colleges NIRF Ranking. Please check it out. link-https://www.shiksha.com/b-tech/ranking/top-engineering-colleges-in-india/44-2-0-0-0.

Yes, you can do the B.Tech Aerospace/ Aeronautical engineering on the basis of Diploma Mechanical. The following are the colleges in Maharashtra offering the asked course.
1. Indian Institute for Aeronautical Engineering and Information Technology (IIAEIT) Pune
2. GARWARE INSTITUTE OF CAREER EDUCATION AND DEVELOPMENT - [GICED], MUMBAI (Bachelor in Aeronautics)
3. Amity University Mumbai (B.Tech Aerospace and Aeronautical Engineering).

In my opinion, you should choose Amity University, Noida. I am also sending you two links for these colleges where you can also check which one is the best. These links help you in taking the right decision. Please check these links. link1-https://www.shiksha.com/university/amity-university-Noida-41334/reviews
link2-https://www.shiksha.com/university/upes-university-of-petroleum-and-energy-studies-Dehradun-30663/reviews.

Hello Hitendra, It's very nice to hear from you that after taking a break of one year you intend to continue your studies. You need to give an application to your college giving reason as to why you could not continue studies and also that you now intend to resume studies. It's in the hands of the management to allow you to study. So do not worry. Best wishes to you.