Diploma

It would be a good decision, you can go for it. It would be more beneficial if you are working currently.

BITS Pilanu offers B.Tech Engineering Technology, a 7 semester Work integrated Learning Programme delivered online designed to provide a broad intellectual foundation and contemporary technologies while developing relevant engineering fundamentals, and introducing the important methods of technology practice. You may look for details of program at: http://www.bits-pilani.ac.in/uploads/WILP_Brochures/2016/B.Tech. Engineering Technology.pdf

Doing 1 year UG diploma from Frankfinn is not at all worth.
You won't be getting good placements as well as salary.

No, as of now you cannot do MBA. For doing MBA you need a degree course as Diploma cannot be considered as degree course, you are ineligible for MBA. Once you complete you BE or any other degree course either through full time or part time then you will be eligible for the same.

Diploma holders in engineering are eligible to appear in JEE (Advanced) by applying in JEE (Mains) 2017. You may refer to following link for details: http://jeemain.nic.in/WebInfo/Handler/FileHandler.ashx?i=File&ii=65&iii=Y

Eligibility for Diploma in electrical engineering is a pass in 10th class. To become a graduate in India, you have to complete 10+2+3 education. Out of this 3-years, the degree must be from a recognized university or equivalent. Your Diploma is not equivalent to a graduation degree therefore, you are not a graduate.