Whilst there is the obvious security issue, I've been told that bmi could end up offering EL AL-esque safety procedures by a contracted firm at LHR, I'm unsure if these safety measures will also be happening over in Riyadh, although I'm sure safety standards there are very high too. There remains a market for flights, as there is a large enough VFR customer base in the UK from Saudi Arabia, and there will also be a fair amount of business pax. I'm sure bmi are hoping on transfer pax also.
I have to admit its a strange market to consider. After all, there are plenty of markets BA have pulled out of besides Riyadh, and plenty of cities outside of India where there is a good mix of business, leisure & VFR traffic. For example, BA's desertion or thereabouts of Latin/South America ...