To some extent, this question is asking for a subjective answer. It's possible to defend slightly different definitions of success for Balram; however, most of them probably involve money, freedom, and/or independence.

The closing pages of the book are a great place to look for evidence of how specifically Balram defines success. Throughout the book, readers have seen that Balram is a very focused and driven individual. His talent was recognized early in his life by his peers, his teachers, and the visiting school inspector that gave him the "white tiger" nickname.

Balram excels in a lot of the things that he chooses to do, but doing well at something doesn't necessarily count for success in Balram's opinion. He struggles against the system that is in place that would keep him a poor servant his entire life, and that is a two-part battle. Success, for Balram, is more than being wealthy. He also measures success with independence, and readers see in the closing moments of the book that Balram is pleased enough with his success to tell the Premier about everything (including the murder). Balram says that he would do it all over again because it gave him a chance to "be a man."

He goes on to close his letter by stating that all of his questionable decisions were worth it for just one minute of not being a servant. Balram has become a titan of his industry, and he is definitely nobody's servant anymore, so Balram believes that he has been very successful.

I'll say it was all worthwhile to know, just for a day, just for an hour, just for a minute, what it means not to be a servant.