Switching Optimize iPhone Storage for photos to Download and Keep Originals - and then back again

I have been using Optimize iPhone Storage on my iPhone 13 for several months now, as my Photos library was taking up too much space on my iPhone, and, since I pay for extra iCloud storage space, it seemed like a good idea to free up storage and keep my originals in iCloud. Last week, I decided to switch to Download and Keep Originals (I did some quick math and estimated that there would be just enough space on my iPhone to download all of my pictures and videos). The downloading went speedily overnight, but then it seemed to stall around 6,000 photos despite having (I thought) enough space left on the phone. Through offloading apps and turning the phone on and off, I was able to get that number down to 1,800 photos, but I eventually grew tired of babysitting it (as it was becoming clear my iPhone thought the photo library was just too big to fit on my phone) and I decided to pause the downloading and reverted back to Optimize Storage on my iPhone. Then, a worry crossed my mind.

My worry is that, because the downloading to my phone hadn’t finished, what if the 1,800 originals that hadn’t downloaded to my iPhone were then added back to iCloud in their low-resolution form from my iPhone, thus “erasing” the high resolution version stored in iCloud. Is this something that would happen? Just having to stop the downloading process midway through scared me a bit.

Anyway, I think I’m safe because the size of my iCloud Photos library remained exactly the same both before stopping the download and after reverting back to Optimize iPhone Storage. But I still wanted to see if anyone had any insight into this. Thank you!