I think that they will more than likely have to find an unknown voice to continue on as a working band. Unfortunately, I don't think that they will be able to go the Journey/Judas Priest route and hire a tribute singer. Another option is to go the Genesis/Spock's Beard route and have one of the other members become the lead singer (I don't know how well their drummer sings or who their drummer is at this point with the various recent health issues). Most of the band members also sing on songs so they could probably pull that off.
Personally, I only recently discovered Saga. I have been a Rush fan for over 20 years, but somehow I had managed to not hear of Saga until about 3 years ago (see similar post in other threads regarding Marillion).
Maybe PA member Melomaniac should apply. He is from Canada and sings and plays multiple instruments and is also a Saga fan who is familiar with their output.