Hi Kate,
unfortunately the provided information is lacking (e.g. index details like partition key, index type, columns are missing) and it is not the DBMS_XPLAN output. However we know that the partition pruning is based on the fiscal year.
You can not make any statement about the original business case, if you change the underlying data structure (global index). De-Partitioning the index does not really make it easier anyway.
>> My idea is to compare the cost with and without index and make index more attractive.
Why don't you do a CBO trace and compare the costs, if that is the reason for hinting the statement?
Regards
Stefan
P.S.: Please think about the 80/20 rule, if the index is a bitmap index.