Is the prayer to be repeated if blood is discovered on the garment after its completion, and are the post-prayer remembrances to be repeated if the prayer becomes void?

There is no need for one who discovers impurity after finishing the prayer to repeat it, and their prayer is valid. As for the post-prayer remembrances (dhikr), they are not obligatory but rather recommended. If the prayer becomes invalid, the remembrances do not become invalid. However, the Sunnah (definition) of delaying them until after the prayer is not achieved unless they are repeated after the re-performed prayer.