They've already said they will offer either rebooking on BA or a refund without penalty for flights cancelled or delayed more than a certain number of hours. They're not offering additional compensation on top of that, or offering travel on other carriers.

It's still going to be a mess, regardless. There are a lot of passengers to rebook. Depending on BA's load factors, there may not be enough empty seats in the next few days to accomodate everyone that still wants to travel.