You could also ask the gate agent to remove them from the flight to sell their seat to a standby/etc, however I don't believe the gate agent can truly delete the reservation (just a boarding pass) without it affecting the rest of the group on the same PNR, or affecting that person's return flight.
Deleting anyone off of a PNR with more than 1 person is possible but I use that term in the most hypothetical way because its just not done in reality. Most systems have some sort of restriction placed on multi-pax PNRs such as you can delete a person but if there are multiple legs you are deleting multiple legs or nothing (hence my recommendation to book O/Ws as well).
Call customer service and explain the situation and that you wish to have one of the six passengers split into its own PRN that consists of just the one way back. Tell them the reason that you want to do this. You are wanting to cancel just the outbound portion of that one PRN so it will not make a mess of the reservation for six people.
PNR?
Correct. You can give the BP and get charged for the flight if you want
You can always print someone elses BP but you cant give anyone a BP without the person being there. No show occurs when a specific person does not board, not when they do/do not print their boarding pass or check in for specific flight.
Nobody here has ever reported having a return trip canceled after no-showing the outbound.
This is written more for the sake of covering every type of situation. If it wasnt written people would abuse it.
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OP - I would strongly advise you to not try this idea. The safest thing to do is to call res and explain to them what is going on and they will give you options what to do.