What if I choose post-graduate diploma in international business operations from IGNOU instead of MBA? Will it be a right decision?

Yes, it will be a good option to pursue post graduate Diploma instead of MBA. But, you won't be able to apply for government recruitment exams. So, I would suggest you to pursue MBA. To work in a private sector, you will need experience along with your degree. All the best.

You can choose for PGDM also. Both PGDM and MBA are equivalent and are treated as equal but in some PSU and MNCs there is requirement for MBA degree. So, preferable would be to go for MBA.