I think it is very much to your advantage that the number of banks (n) is larger than the time period (t). When dealing with panel data, the size of your dataset is important; and, if you are dealing with a very large dataset, you can then actually run two tests. The first test can comprise only the balanced sample. The second test could then be the entire unbalanced sample. The results you obtain from both tests can then be compared as a robustness check.
Working on PHD proposal "Integrated Model for Assessing Innovation and Entrepreneurship levels in Cooperatives Financial Institutions". Any interesting articles that may be of interest?