The only way a battery could be reverse charged is if it was dead when it was attached to the charger (or brand new and never charged). Sounds like that happened here. I wouldn't trust that battery after that sort ordeal. It would have to cause chemical changes to the plates that are unlikely to reverse completely. In a normal battery, positive plates are made of lead dioxide, negative of pure lead. reverse charging would cause oxygen to migrate to negative plate. Then recharging would push it back. That's in addition to the battery having excess sulfation due to being fully discharged, not to mention heat damage from the recharging process. What you end up with is a questionable mess.

As for damage to the car, if there's a master fuse or fusible link, that would protect everything. That isn't the case with older Benz cars. The alternator is connected at all times, so that's where I would expect first damage. When the connection is "normal", the alternator diodes block current flowing back from the battery. Reversed, and the battery would essentially discharge through the alternator stator and diodes. If that goes on long enough, the alternator would cook off. If you turned the key, then the possibilities are endless.