Spells with the breath weapon keyword have a chance to be re-used during battle. Each breath weapon spell lists the chance of re-using it (usually 16+). At the start of each round after you've cast the breath weapon spell, make the re-use roll. Success indicates that you may re-use that spell as a standard action, but for that round only. If you fail the re-use roll, you don't have the option to re-use the spell, but you get another chance at the beginning of the next round.
The breath weapon power lasts for a single battle only.
You can have only one breath weapon spell active at a time. If you cast a different breath weapon spell when you have an earlier spell active, the new spell cancels the earlier spell. (See the Chromatic Destroyer Heritage talent for the path to multiple breath weapon spells.)
Failing a death save cancels any breath weapon spells you have active.
Failing a death save no longer cancels your breath weapon spells. Keep rolling the entire battle.