I am always in favour of having a window for legalizing black money. But that should offcourse come at a higher cost/penalty. And also there is difference in black money. In our system, lots of businesses accumulate black money due to not paying taxes properly. They should be allowed to legalize it through penalties.
Money earned purely through bribe should never ne allowed back. That could be brought back through legal actions and maximum amnesty could be provided for limited periods to surrender their money earned purely through corruption. Even if they are allowed to retain 50% of such money, that only makes bribery more costly, but the business continues.
At last there is some ammendments coming up on this issue in budget:
Finance Minister