That’s a good question.

You need to think of your assets like you would APIs. You can’t just turn off an API and replace it with a new one, because you must assume that users keep browser tabs open for days and may be making network requests against ‘old’ APIs, just as they may be making requests for assets that are now ‘old’.

So, you need to either keep assets around, or handle 404s for assets by prompting the user or just doing a full-page refresh, or a bit of both: keep old assets for a few days, and handle 404s as best you can.