They needn’t drop the shows already produced. Just produce another show where she is seen waving goodbye to someone as she leaves for somewhere, and she tragically gets into an accident, or suddenly an un-diagnosed problem causes a premature death. Then - ON WITH THE SHOW!
They haven’t dropped When Calls The Heart, just put it on hiatus. According to Hallmark’s statement, they are looking for a way to extract her scenes from episodes already shot.