Whether ex wife can file false cases of 498 or Dv or any other case after passing divorce decree in court.

yes, if you obtain decree in ex-parte, if it is contested divorce.... then no problem

498A can be filed after marriage subject to the limitation period.

If the allegations pertain to period when she was married to you, and it has not been 3 years since then then she can file such a complaint, however it would be very feeble. In cases where complaint as regards allegations have been made even after 3 years of happenning - court has the power to condone delay. 

Dear Bharatji

As per your reply, Any ex -wife can file any case of any allegation regarding matrimonial dispute (498A/DV..) even within 3 years after passing the decree of divorce ( mutual or contested). Please confim.