C-160 Transall is an old plane and we have C-130J which is more suitable than C-160. What we now in quantity is Strategic lifters like C-17 Globemaster or the likes of it. What should be asked is If it can be possible to shift the line of C-17 to India, we might be having more requirement than mere dozen. BTW would C-17 body be capable enough to have AESA antenna on it to be used as AWACS?
It's not financially viable to restart the line AND transfer it. India should be more decisive with their procurements, Boeing was basically begging for orders.
Minimum 50 orders would be needed.
The US Military operates well over 200 of these right now, and they are relatively new aircraft. I'm guessing there won't be any plans on replacing these for a few decades at least. It is a shame they discontinued this plane, it was very versatile.
As @Ginvincible said - they will serve for at least 30 years from now. Even more probably. Not much changes in transport aircraft as long as they can haul a big enough load from here to there. C-17s the world over will undergo certain electronics-related upgrades (maybe even an engine change over to a new type) over the course of their lives. But a replacement aircraft is unlikely to emerge for a VERY LONG TIME.
Heck - forget the C-17, a replacement for the much older C-5 is nowhere on the horizon!
What are likely to emerge though (as far as USAF transports go) are further improved variants of C-130J, and certain specialized transports for Special Forces use - with an emphasis on reduced radar & infrared signatures (and improved STOL capability) to assist in large scale para-drops of troops in a hostile territory from altitude.
^^ Speed Agile concept
EDIT: Also, I foresee a requirement to emerge regarding the capability to vertically lift heavy cargo (much more than what a V-22 can manage), sometime in the 2020s.
Russian design :