It is an acquittal in 498A, may be because the prosecution could not prove beyond doubt, hence any counter case will not be meaningful. Moreover, how come your father in law has filed cases against you?, what about your wife, has she not come into picture?, you have stated that only Sec4 of DP act is pending?, what do you mean by that?, whether that case has been filed separately other than 498a? What is your lawyer's opinion?, in any case no case for defamation will be maintainable. Moreover your action may prompt her to either go for appeal or file a fresh case within her jurisdiction and also mshe may file DV case too. For the present wait and watch the developments silently.