Validity of the will if the witness who signed is expired

If the testator still alive let new Will be drafted with 2 new witnesses and let this new Will be registered with sub-register. If the testator already dead, the Will should be got probated in the Civil Court to execute the Will, the proof of Will with help of other witnesses who can be members of family of the testator can help the probation of Will.

If the testator is no more and the witness/es are also no more then the witness's legal heirs can be summoned to verify their relatives signature in the will and prove the same in the court of law

First of all, for any Will to have a proper execution, the Will MUST have atleast 3 signatures, one of the testator and minimum two of attesting witnesses.  Note, two attesting witnesses are required for a Will to be valid.

If one of the witness has died, its not a problem because if the second witness is still alive then that person can come to court and testify about his signature and testators signatures.  

If both witnesses are dead..then Will is proved by other corroborative evidence.  So, death of one attesting witness doesnot make a Will invalid.