This shows how bad it is.
I measure a short between VBAT and VSWITCH so this must have caused the motor to keep running.
I can't imagine the RCM playing a role here, but maybe a sticky contact there caused current to jump on a weak spot like this switch.

Now getting a replacement is a challenge. I need connectors and A 193 545 03 04 (the A 1935450004 is for US with 12 fuses) the 0504 is RHD
Mercedes part A1705450104 is confirmed to work but may signal a lamp warning on reverse (from german forum)

Inside of the light switch