Answer
(Fatwa: 452/408=D)
For a nikah to take place it is necessary that it is done in the presence of two sane and Muslim witnesses who can understand the procedures of nikah:
قال فی الدر: و شرط حضور شاھدین حرین أو حر و حرتین مکلفین سامعین قولھما معاً علی الأصح فاھمین أنہ نکاح علی المذھب [الشامی: 2/296]
In the abovementioned case, when you can not say with surety that the two witnesses were able of being a witness or not, then surely the nikah can be regarded as neither valid nor invalid. Therefore it is better to avoid to have any relation i.e. if you like to continue the relation then you should renew the nikah and if you want to discontinue then you should terminate it by talaq out of precaution.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband