My voice teacher has done rehabilitation not only on performer's voice, but on her own, as well. She had a stroke and had to learn to sing and talk again, which included returning to the opera stage in Europe and the US.
When you can use the cords again, she says to begin with just humming a short note pitched slightly above the speaking level. Gradually lengthen the hum in duration and build the muscles up again day by day with the single note humming.