Dont get too excited, going off recent responses to problems ie weather, I suspect that the airlines will just cancel all flights as the logistics of operating any sort of transfer of services will just be too great to manage, eayjet and Ryanair will probably shut up shop for the day as will BA European and Domestic. With notice I think the long haul airlines will either cancel or delay flights. The only way other airports would benefit is if there were wildcat strikes and flights were already airborne.
Just my opinion