I say, with Allah's guidance: It remains pure and does not become impure due to necessity, and there is no difference in this between wet and dry, intact and broken, unless it is a lot. The criterion for a lot is what the observer considers abundant or if a bucket is not free from it. The same ruling applies to everything that cannot be avoided, such as horse, mule, and donkey dung, cow dung, and bird droppings. See: Maraqi al-Falah p.39, and Allah knows best.