If there is any damage on the bus, especially paint transfer matching the colour of your car then most of the larger bus companies will usually arrange for the damage to be repaired, as a long drawn out legal battle with your insurers will usually cost far more than a new wing mirror and paintwork.

I work for one of the large multi national bus operators, and in situations like this as soon as the company becomes aware of any alleged collision, all vehicles operating on that particular route at the time in question will be traced and examined by a supervisor as soon as possible. Any damage found is photographed, cctv footage is examined and the driver will be interviewed. If they admit liability, they will arrange for repairs to the vehicle and arrange a courtesy car at no cost to the claimant.

It sounds to me like there could well be some paint transfer between vehicles, if the paint left on your car matches the colour of the bus and vice versa then I would imagine that they will admit liability fairly quickly, as the sooner it is sorted out the less it costs. If it is a small independant operator, they may not be quite as cooperative.

One more thing, if the bloke who witnessed this was at the bus stop opposite from where this occured at 5AM, try going out there at the same time tomorrow and see if he is waiting to catch the bus again, he may give you his details as a witness.

Just remember before you go down the route of claiming off your insurers, it is a no claim bonus, not a no blame bonus. May end up cheaper in the long run just to take it on the chin.