Welcome to FT!

Did you check the o/w fares for a ticket Europe-USA? Most likely it will be quite high/expensive.

Better contact LH after you have flown the outbound (when travel has commenced LH can deal with your ticket and you don't need to contact Exp) and ask for a separate PNR to be created for the person that needs to be rebooked. Any LH agent knows how to do this. Then you rebook the return flight. Presumably much cheaper than buying a o/w ticket.

You def. don't get blacklisted for missing a return flight. Happens every day. People get sick, get up too late or miss the airport bus/train etc....