The answer to your question can be found on the Monkey Trivia
"I spoke with a member of the then "Saiyuuki" staff and he told me that when the show was first pitched no one thought it work. However, the reality was that it was a huge success, garnering over 30% ratings. After the first 26 episodes were aired, a continuation of the story was planned, but this time with high expectations in light of the success of the first. However, that was not the case. The second 26 episodes did not do as well as the first and no plans were made for a third series. Also, by the time the first series and second series had aired, the actors became very popular and their schedules filled up quickly.
Basically, they moved on with their careers.
As for why the group never reached India, perhaps it was because the production group had planned to stretch it out for longer that they may have to gotten to that point in the second series, but because the ratings were not as good for the second series (less than 20%), it just never came to be.
But the answer I received was that rather than the goal, the process, the adventure was most important -- fighting evil, helping the poor, etc."