If the brackets can't be sprung far enough apart to allow removal, then looks like you could remove or loosen the screws holding the bracket to the valance. Remove the end with the smaller, round pin, the one that doesn't have the spring. You should then be able to roll up the shade. Then install the shade and bracket back in place, when you pull the shade down it should wind up the spring to retract the shade. You might have to put a few turns into the spring when you remove it, depends on how much tension was released when it failed.
It would be easiest if you can remove the shade with screws only loosened, it will be easier to reinstall if the bracket is not completely removed.