To close this out, I had a callback and spoke to a very friendly agent who was in a managerial position.

The LHR-LAX flights were originally there (7 for use with Avios in J). Within 12 minutes, the flights in J and W for use with Avios had done (side note, I've seen almost all award flights in J pulled between the 22nd and 24th December apart from 3 routes (BNA/DEN/NYC). The agent did things to the law and didn't hold seats. I was told almost all agents will hold seats, but officially they are not meant to. Revenue Management refused the request to release any seats.

We are now flying:
LHR-DEN
LAX-LHR

The cancelled ASP-LAX (not DEN-LAX, sorry) was not available in economy anymore, only business (with Avios). The cancelled LHR-INV flight was not available in any cabin (with Avios). BA covered the cost of the ASP-LAX flight in business which would have cost 33,000 Avios + £9.20 (so revenue management really didn't want to give up these seats from LHR-LAX).

So there you have it.... I will always make sure the agent holds the seats in the future (even though it seems they are not meant to). We are now booked under RFS at a cost of 70,000 more, but when factoring in the 10,500 Avios spent from LHR-INV and 18,000 Avios from ASP-LAX, I'm 41,500 Avios down with £440 cash refunded (now RFS), and £70 hotel in Inverness refunded - as well as flying from ASP-LAX in Business. Of course I still had to pay the change fee, but I would have done that anyway.