We ride and walk the C&O frequently. Yes, that would be an excellent option for evacuating without a vehicle.
Helps that the C&O starts out in the least crime-ridden part of town, too.
I have a C&O map, will dig it out and keep it handy.
Bikes, motorcycles or a really good driver with a SUV and proper tires should have no trouble depending on where one would get on/off the Towpath and how far you wanted to go.
I've seen ambulances and ranger vehicles on much of the towpath.
Don't forget the "Rail trails" and other hiking paths.