According to me, even after all conditions are clearly mentioned in the MCD settlement agreement, your wife can still file cases of dowry harassment and domestic violence against you and your parents and get you arrested. The police will usually blindly file a case and arrest you. The onus is on you to prove yourself innocent in court. It is a different issue that later, the allegations may not be proved in court and after a long time you may get relief. But for the time being, your wife can certainly make life miserable for you and your parents.
Also, she can claim enhancement of maintenance amount from time to time and the court will allow the same. Even if she has agreed for zero maintenance, the court will allow her to apply for enhancement and you would not be allowed to refuse. The court will take into account your salary, all your assets, inherited property etc. and decide on the alimony/maintenance amount in such a way that your wife's lifestyle is equivalent to yours. Since, your wife earns less than you she will certainly benefit a lot and you stand to lose.
I suggest the following measures to be taken. Rest is upto you.
1. Immediately ask your parents to put an ad in the local newspaper disowning you. Hence in case 498A is filed against you and them, they cannot be arrested as they cease to remain family members.
2. Since your wife is staying separately, immediately file a case in family court for "Restitution of Conjugal Rights" asking the court to direct her to join you back. By doing so, you will be in a much better situation in case your wife files for divorce.
3. Forget about divorce. Make a strong determination that you'll not divorce your wife till your last breath. As per current laws in India, divorce will only benefit wife. Husbands lose everything, money, time, respect, peace of mind etc. You'll see your wife walk away with half your assets and you cannot do anything about the same.
4. You should have not slapped your wife. Anyway, now that you have done it, learn to deny it. Convince yourself that no such event ever happened. In the court also, you should deny this and ask her lawyer to prove it. If the incident occurred within the 4 walls of the house and there are no eye-witness and your wife had not filed an FIR immediately after the incident, it may be difficult for your wife to prove that you slapped her. Stop apologizing to her in front of her relatives and start denying the incident openly. Do not chicken out in a weak moment. The good part is law in India relies on evidence and not emotions.
5. If your wife files for divorce, contest the same. Do not agree for a divorce. Your parents are right. Consider it fate. But you need to stick to your wife for life. Do not divorce her. No matter, how smart your lawyer is, it is well known fact that in all divorce cases only wife benefits while husband loses. So, stay away from divorce and resist it.
6. In future, if your wife returns to stay with you, install CCTV cameras in your entire house so that she cannot purposely injure herself and call the police and blame you. You will have to stay vigilant for a couple of years till your wife accepts in her sub-concious mind that you are smarter than her and that she can neither legally harm you in any way nor can she extort money from you. Eventually, she will start respecting you and love you.
In the interim, if your wife files 498 A against you then you may have to visit the police station a couple of times but make a strong resolve that you'll not fear the police and will not succumb to pressure. Rest assured, convictions in 498 A is less than 2% since court only relies on evidence to conclude wrongdoings. Make a strong resolve not to divorce your wife. Be a man and rectify your wife. Only cowards think of divorce. Also what is the guarantee that after divorce, your next wife would be better than the current one?