Right - sometimes the fare rules say it's nonrefundable after the first segment, but I just checked a r/t EWR-LHR itinerary in May and it does allow refunds. But every fare could be different. Still, that refundable fare does say in the Penalties section that it will re-price the segment that you did fly as a one-way, and there's a very high likelihood that will cost more than the round-trip, so you wouldn't get any money back (unclear if they would try and charge you the difference, but probably not).