Thanks
Ralph


That's a tough one. If the thumb latch broke while the mortise was engaged with the keeper, then there's no easy way to get it out.
Your best hope is to try to maneuver the broken thumb latch back in place and try your best to throw it manually. Try pliers, screwdrivers, anything you can to get that hook to flip.
If nothing works, then your only option is to find some way to cut the hardware out. This is a very difficult project and we highly recommend the help of a local professional to come out and assist you.