You say that you were on medical leave for about 8 months during last year. It appears that after rejoining duty after the said medical leave, you again entered leave and have been absenting for the last 6 months and would not be able to join duty for the next 6 months. That shows that your effective service in the Bank during the past 4.5 years is only a little over 3 years. The Bank could have terminated your service even without the disciplinary action by invoking Cl. 17 of Bipartite Settlement for voluntary cessation of service, if you are a workman. and I presume you are a workman covered by BPS.
Please further note that confirmation in the Bank after probation does not confer upon you any right to violate Conduct Rules. Confirmation does not release/exempt you from following the laid down Conduct Rules.
The fact that you remained absent for a pretty long time and also do not wish to join within the next 6 months suggests that you are not dependent on the Bank job that you are able to survive without salary as the Bank does not pay salary for such absence.
If the Bank has initiated disciplinary action against you, the best option for you is either to rejoin duty immediately by offering satisfactory explanation to the Bank for your long absence.
Quit the Bank gracefully by submitting your resignation letter and requesting the Bank to drop the disciplinary proceedings to avoid any blot on your personal profile that helps you seek employment elsewhere. Good Luck to you.