Whenever it shall appear to a probate court, before which a purported will has been presented for probate, and whenever it shall appear to the superior court, before which a petition for probate of a will is pending on appeal, that a will cannot be proven as otherwise provided by law because one or more of the subscribing witnesses to the will, at the time the will is offered for probate, are serving in or present with the armed forces of the United States, or serving as merchant sailors, or are dead, or mentally or physically incapable of testifying, or otherwise are unavailable in the course of their service, the court may admit the will to probate upon the testimony in person or by deposition of at least two (2) credible disinterested witnesses that the signature to the will is in the handwriting of the person whose will it purports to be, or upon other sufficient proof of the handwriting. The foregoing provision shall not preclude the court, in its discretion, from requiring in addition, the testimony in person, or by deposition, of any available subscribing witness, or proof of such other important facts and circumstances as the court may deem necessary to admit the will to probate.