Pretty much imposible unless you have direct access to a Pornhub data center. One way to remedy this though is by regularly downloading you favorite videos.
If you find a video you like, and think it's at risk of being deleted, download it. There are a lot of browser extensions that allow you to download from Pornhub without logging in. And for storage just buy two cheap HDDs so you can run them in RAID 1. That way if one HDD dies you still have the data safe on another drive.