All materials you have purchased stays in your account for as long as the Elite Notetaker has not removed them. So if you ever close out of the document just log back into your StudySoup account and you will find all purchased materials listed here.
All annotations and highlights might not be saved if you closed out of your document, but the material itself will be there. You will likely not be able to access your materials after you terminate your account. We suggest you download them first.