What is the procedure if one of the two witnesses dies before recording his testimony or refuses to give it?

If the witness dies before testifying, then either he had two witnesses attest to his testimony, in which case those who heard the testimony can bear witness to his testimony. And if he did not have them attest, then the claimant is left with only one witness. In this situation, if the defendant takes an oath, the claimant is left with only the oath [for himself]. And if the defendant refuses to take the oath, then the claimant takes an oath in addition to the witness.