OU TORAH Yevamos daf 121 Endless Waters and Nowhere To Be Found By Bais Havaad Halacha Center

Rav Yitzchak Grossman says if we have not heard him is that a heter to remarry its a machlokes.The Poskim says nowadays we have electronic communication that would tell us if someone who can't be found is alive therefore we can assume he is dead we can be makil and allow the wife to remarry.for the rest of the shiur click here.