The tab won't go away, but it will trigger a fresh http request (and thus any input in a form will disappear), I believe the behavior is the same on iOS for iPhone.

The parent likely means background killed in the sense that iOS fairly aggressively removes loaded web pages from memory and replaces them with a screenshot and a url. Most of your 500 tabs are likely screenshots and urls. When you select them they fetch the page from the server fresh.

In most cases this is fine and frees up memory for other apps/tabs, but with web apps with local state, said state gets clobbered in a way that never happens on a desktop browser. Because it is fully automatic you can never really tell or trust that local application state will still exist if you tab away and back.

By “killing background tabs” the parent simply meant that Safari wipes loaded tabs from memory, so the tabs have to reload when selected again.

However, in rare cases if you’re foolish (aka me) you might:

1. Unintentionally open a new Safari window via iPadOS multitasking.

2. Unintentionally close the original Safari window with your 400+ tabs.

3. Lose 400+ tabs permanently.

I’ve learned the hard way to just use the Reading List.