WHBM
Althouth I'm not BA ops but based on my extensive experience of handling similar things I can tell you a few problems in your scenario:
1. Insurance. Russian carriers (excl some majors) have a different insurance policy and even then it is hard to get any compensation. If something happens it would cost BA a fortune in lawsuits.
2. Service standarts. Most of operational IL86s are deployed on charter routes and in a pretty sad state inside. If someone think that *unnamed* G-registered charter 767s are cr@@ inside they never seen Russian charter planes.
3. Believe me - the realistic time take to get IL86 airborne from Moscow is 12 hours or more from signed contract. IL86 operators are not specializing on a short-notice business.
4. IL86s are banned from Europe due to Stage II anyway.
5. Potentially there could be some passengers onboard who cannot travel on Russian airlines apart from a few majors like SU or UN due their corporate insurance policy.
6. It is usually cheaper to fly your own airplanes (if availability and timescale allows) than chartering someone else.
On the other hand there is VIM Airlines in Russia operating a fleet of 757s (tight charter config anyway) who are normally quick to react and there is Transaero with ex-Virgin 747s and well known for changing the planes assignment between routes on an hourly basis
. One of them or combination of them may work but introduces some problems and uncertaincy anyway, let alone the cost, so from my point of view BA ops did it in the right way.
