When you fail to write a scroll because you ran out of ink, it will become a “garbled scroll” instead of disappearing. Garbled scrolls can’t be read (or possibly they could be read, for a number of generally negative weak magical effects), but they can be re-blanked so the scroll can be written again. This could also happen when you fail to write a scroll by not knowing it. There is a slim chance, probably less than 10%, that you end up writing some random scroll instead of a garbled scroll.