It is a rescue mission. The original mission was supposed to be a couple weeks and that extended to nearly 8 months due to unrecoverable issues with Starliner. That’s not a crew rotation, it’s a major failure of Starliner. As for the escape option while docked, even a leaky boat is better than no boat if the ship is sinking, but the fact is NASA elected to not return the crew on Starliner for safety reasons.