Most marriages in India, particularly among Hindus, are not registered. If proof is required to establish a marriage, one will have to resort to things like "Wedding cards", guests, who attended the marriage as witnesses, the priest who performed the marriage photographs, videos etc. The parents of your wife and her other relatives can easily establish the marriage. It is easy to prove a marriage in the near past than one in distant past. There will be at least a small group, who attended, if there was a marriage function. If you were physically present at the marriage function, things like your going abroad or non-consummation cannot be the ground for denial of marriage. Non-consummation may be because you did not take your wife with you.
If it is only six months since your marriage why your in-laws should unleash 498A and DV Act against you. Are they professional marriage cheats? If not what other reason have they got?