Lufthansa is flagging you a no-show and cancels your return flight without warning or reimbursement. I didn’t like them before, but after doing that I will never set a foot in one of their planes.
I had a international flight with the last leg being a bus ride from Munich to Nuremberg after a 7 hour layover. I opted to take the train that got me there considerably quicker.
On the morning of my return flight when I was about to check in the lady at the counter told me my booking is non existing. That fun trick by Lufthansa cost me 600€ extra.
But I know that is just a little price compared to the emotional damage that poor little company was caused by me…