Victims of child sexual abuse who missed deadlines for filing civil claims against their abusers may get a two-year window during which they could bring old cases to court, under one legislative scenario under discussion on Beacon Hill. But any nonprofit held responsible for the sexual abuse of a minor could not be held liable for more than $20,000 in damages, the existing cap. Lawmakers are in the process of scaling back a proposal, actively opposed by the Catholic church, that would have made sweeping changes to the legal remedies available to people sexually abused as children.