Oral testimony of a lost revoking instrument is not admissible to defeat an existing valid will. A revoking "other writing" must be executed and proved in the manner required by the Wills Act.
Leonard Estate, 427 Pa. 363, 234 A.2d 856 (1967).
Robert A. Kelly,
Wills - Lost Revoking Instrument,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol6/iss4/6