It's fair to say that a good 25-33% of flights from this country that are heading southbound could still take place virtually risk free at a lower level. I'm not saying my numbers are correct but an example might be: A departure out of Gatwick could trod along 100 nm south at 6000ft before being out of the risk zone and then climbing higher and proceeding normally. Clearly this means temporary changes to airspace classification across borders which would affect GA but thats a lot better than having commercial traffic at a complete standstill for a month!
Is the risk not from 0 - FL280