witnesses of agreement

Dear Sir,

I purchased about 5 Kanal Land in 2013 from one of my relatives, in presence of two witnesses and notary public verified the same sale agreement.

On the base of that sale agreement, we put a civil suite in session court for Khata. Currently, the case is on witnesses stage & one of our on the witness who has a signature on sale agreement is not appearing in court for witnessing.

Please guide me what would be effect on my case or what would be the effect on sale agreement, if one witness is not coming in court.

My advocate said me, we can lose the case if one witness not coming in court for witnessing. Is it true? Or is it must both witnesses should be witness the sale agreement or one witness and notary public is enough for proofing sale agreement.

Thanks in anticipation