Complex sentence: When Melchior reaches town, he sends a message to Ilse to have her get Wendla to meet him at the cemetery at midnight, but she can take no action as Melchior "hasn't heard" about Wendla.
Split into simpler sentences: When Melchior reaches town, he sends a message to Ilse to have her get Wendla to meet him at the cemetery at midnight. But she can take no action as Melchior "hasn't heard" about Wendla.