Firstly, sorry for your loss!
As another Las Vegas resident I'd say that it's highly unlikely in my opinion that there will be any direct BA flights from LAS to London in September. In terms of getting back to the UK you'd probably be looking to fly either via LAX or ORD or DFW. Given the $400 credit you have with AA I'd probably be looking to not only book with them but also fly with them. If you can fly with AA on their 777W aircraft then I'd probably choose Premium Economy with AA over WT+ with BA, and the fact that AA are also serving hot food instead of just a boxed up picnic is something to bear in mind too.
The only downside at the moment is that schedules are all over the place with very few direct flights meaning you'd need to fly through an AA hub to get to most places. LAX does now have some direct flights, as do DFW and ORD but for most other places you'd probably be looking to flying through PHX or DFW.
Hope that helps!