Can one leave IPM after first 3 years (after receiving the BBA Degree) ?

YES, One can do that but there are some complications which makes it, not a good thought to be practical enough.

Basically, one can leave the programme after first 3 years of IPM, but, it is a 5 year programme, therefore it won't give any certification or testimonial of 3 years of study at IIM.

Therefore, one will be left only with IGNOU degree and 3 years of IPM education that isn't even certified.

So, leaving mid-course will leave one high and dry and also since the only certification one will have is from IGNOU. Hence, it may not be advised to leave IPM after 3 years.