validity of merged bank cheque

What is the problem you are facing

Left over cheque leaves has to be honoured by merging bank.

Contact new bank, where Dena Bank accounts have been transferred in consequnce to merger.

Contact bank they will provide  new cheque return old cheque.

You can very well initiate action under section 138 NI Act against the drawer of the cheque for issung the invalid cheque because the merger took long ago, whereas the drawer has issued the cheque only recently therefore he is liable for the consequences

Yes, you can initiate proceedings  against drawer not only for cheque bouncing case but also for cheating. 

If you have that cheque you have to present it within time provided by bank after the time is lapsed it becomes invalid ,issue notice and file cheque bounce case.