Given their low orbit, it would make the next couple of decades (?? offhand, I'm not sure how long it would take for the debris to completely de-orbit and some of the results are going to be more energetic after any attack) really suck... The resulting loss of life as a result of inability to launch new storm tracking satellites alone should warrant the death penalty for anyone involved in such an intentional attack.
Should be 5 years or less, that's why SpaceX put the satellites in low orbit, the atmosphere cleans it up. Also a low orbit debris cloud wouldn't prevent launching new satellites to higher orbits, the probability of collision just passing through would still be negligible, it adds up as you spend time in the polluted orbits. There are a lot of misconceptions about space debris.
5 years if __intact__ and simply inoperative. In the event of a collision or attack the objects will break up, and the energy is not evenly distributed. Some pieces end up with lower energy and decay faster, others greater energy and thus higher orbits.
https://en.wikipedia.org/wiki/Kessler_syndrome cascades can result and even spread to higher orbits. As an extreme emergency measure it might even be wise to de-orbit everything in attempt to mitigate the damage.
Wrong. You cannot execute an orbital change with a single application of delta-v. Any pieces can at most end up in a new elliptical orbit where the high point is further up and the low point is where they started, and this subject to the same atmospheric drag there. It takes a second application of energy at the top to circularize into a new orbit.
Operating satellites at that altitude would become dangerous, launching through it would be no problem. Debris decays more quickly the lower it is in the atmosphere (the thermosphere extends to ~600km for example).
