The issue of adultery, if you can prove that they stayed together in the same room of the same lodge at the said outstation, it can be considered as an act of adultery and can very well seek divorce on that ground also. If she has withdrawn from her agreement for mutual consent, you may use this ground as an addition ground for contested divorce suit. If, by filing 498a case during the pendency of divorce case, she tries to extort money using this as a black mail, do not budge to the pressure tactics adopted by her, instead you may challenge all her false cases on merits from your side. consult your lawyer on further issues and proceed as per his further advise.