I’m not sure what you mean by “web-archive”. I can’t find any reference to it in the journals, is it a browser related thing or some external program/app?
I use Chrome on a PC, and it has the option to save a “Webpage, complete”. It creates an html file of the page, and a folder that contains all the files that make up the page. These saved copies are on my hard-drive, or wherever I tell the browser to save it (like a pen-drive, cloud storage, network folder, and so on). I would imagine this is the case for your Mac too, but you would need to talk to a Mac user to be sure.
I’m pretty sure iNat do backups of journal content, so the chances of losing your content is very low. If you are talking about incremental backups, such as backing up “versions” of your post before making substantial changes, then it might be better to develop the document in a word processor that manages changes (called version control), and then publish the final result into the journal space in iNat. If you are already familiar with a particular wordprocessor, then you have the added advantage of a familiar interface that allows you to focus more on the content itself