I apologize for not including enough details in my earlier posts. Yes, we have different tickets. Our cruise is actually going from Barcelona to Dover so the LHR to BCN is 1 way and was booked separately from the roundtrip HOU-LHR. Because I was using Avios/Companion fares for the long-haul, I had to book those on the website. The website would not allow me to do IAH-LHR-BCN then LHR-IAH all on the same avios/companion ticket. It saved us about 10k using Avios and companion fares (there are 4 of us) so I suppose it is worth it having to either pack lightly or go through security versus having paying full price.

Thank you for your responses and the information. It sounds like I will just have to pack lightly or do the security dance/luggage pick up/drop off at Heathrow since it sounds like BA won't check "through" luggage on two different tickets. Fortunately, we are in Barcelona two days before we cruise...although, I still worry that might not be enough time if they do lose our luggage. First stop is Gibraltar. We can do laundry once on the ship so I guess I will just have to pack enough clothes in our carry-ons to last us until we get on the ship in the event our checked luggage is lost.