ATTESTING WITNESS TO A WILL NOT AVAILABLE

At the time of filing a probate op one of the attesting witness to the will signed affidavit of witness at the time of evidentiary hearing the whereabouts of the attesting witness is not known ( probate filed in the year 2012 the case s coming up for hearing in 2015) now the whereabouts of both the attesting witnesses not known to the petitioner. what is the remedy available for the petitioner? can the testator s wife file third party affidavit at the time of evidentiary hearing to substantiate the execution of the will ?