I truly doubt TATA will buy out NML . . . they need a local operating company with local ownership and participation of locals. Buying it all and then being owned by Indain company TATA may prove tough in dealing with native issues as well as the unions involved.
No while TATA may want to they know it would not be in long term interst.
This being said they may try to have more ownership then the 29% they have but that would be it.