If a pattern is on Ravelry and it’s free, you MUST add it to your library in order to retain it. If it is later changed to non-free or even no longer available, if it’s in your library, you’re fine. It will stay there. If you just queue it or favorite it, it is not in your library.
Ravelry makes it hugely convenient when the pattern is sourced as a Ravelry download. You can just add it to your library. Unfortunately, many people think that it’s saved to their library when they favorite it and that’s just not the case. It MUST be added to library. Just clicking “Download PDF” doesn’t add it to your library. You MUST click “Add to Library”.
If you go to Ravelry and the pattern information is just databased on Ravelry but the pattern itself is on a different linked website, no amount of favoriting or queuing will ensure that you have that pattern saved. You must go to the website and download it to ensure that you retain it.
Remember that there are no guarantees on the internet. You can pin them or bookmark them all you want but that doesn’t mean they’ll still be there when you go looking for them again.
You see what I said about there being no guarantees, though? We could all wake up tomorrow and there could be no more Ravelry so you may want to consider downloading anyway. Obviously unlikely but it could still happen. The only one you can depend on is yourself!