There can be several reasons why a webpage is not available. Apart from the obvious server outage, there could be a geo block or a recent deletion of the page.

As long as you are able to get the address of the webpage there is a good chance to retrieve it.

One possibility is to use https://cachedview.com/ which allows to view cached pages from Google web. It is usually updated every few days by google so as long as an article is a couple of days old, you have a good chance accessing it there.

Another option is https://web.archive.org/ which archives copies of webpages including old versions. So if you want to know what was on a certain webpage years ago, archive.org is a good start.