File for anullment of marriage on grounds of fraud 

rely upon letter from wife that she was forced to marry you against her wishes and that she may commit suicide 

Hi, you can file a contested divorce petition on the grounds of non- consumation of marriage and mental cruelty 

you can file a petition before the family court for dissolution of marriage. As such it takes about 3-4 months if she is absconding, if she comes to contest the matter it will take considerable time

If you have disclosed facts about suffering from spondylitis no case of cheating is maintainable 

since her missing case is pending, the case for divorce won't be filed since the other party has no address and until she is there. it is hard for the court to entertain your case. 

if she commits suicide there is no risk for you since a missing case has already been filed and you are not in contact with her, further, she is not at your place i.e. with you which can make court presume that you are the reason for her death. 

body injury or some disease cannot be the reason of misrepresentation, it only happens when u take any good or service from someone and pay the price against that. since Hindu marriage is not a contract your laws can never file a case against you for cheating or misrepresentation.

However, you should also get a case filed her of her missing if the father's complaint makes you the culprit. it is requested that do not throw away the reports showing your wife insane and mentally unfit as this can be the ground for divorce. 

First you search her that will be prime priority to protect her from doing suicide and later on you can go for annulment of marriage once you handover her to her parents.

Hello

1) Mental depression in itself is not sufficient reason for annulment however, the fact that she did not give her consent for marriage can be foundation of annulment of marriage. Pendency of missing case is irrelevant.

2) No cheating case can stand as you head revealed your health conditions to her before marriage. It is important that she has stated in her letter about your illnesses while admitting her being forced into a marriage. This can also be interpreted as the cause of her disappearance. You need to have your defence ready.

Hello

        A vital fact was hidden from you before marriage and hence it is a strong ground for divorce and therefore you shall get divorce on this ground. The fact that she is absconding and her parents have themselves filed an fir stating mental disorder is proof of the fact that she is mentally unstable.

Back pain is not something that affects the marriage directly and it is not a major disease. It is happening to most of the people nowadays.

Regards 

Yes you can file an annulment of the marriage on the ground that in marriage the facts of her condition was not disclosed you were cheated and she was forced to marry.

See if it was informed they cannot file case on same while since you have letter as proof from her even if she commit suicide and she is not mentally well then there is no risk to you.

You can file for annulment. Annulment case and Missing case is not connected. Also, since she admits that she was forced to this marriage, it will be a strong evidence for annulment. If the letter is handwritten by her and signed by her then it's even better.

No risk if she commits suicide. Make sure you keep the psychologist report.

The court may ask as to why did you not give the missing complaint, so do take the details of the complaint from your FIL. Also, make sure you go to the police station and give a copy of her medical report as to aid in her search. This way, her mental condition I will come into picture, and if she commits suicide, you will not be held responsible. Also you will be included in the missing complaint of your wife. So that if court asks then you can say that since your FIL gave the complaint you decided to join them and co-operate in the search/investigation.