How to force cached index.html to be forgotten

By mistake we let browsers to cache index.html of our web appplication without any expiry setup for a few weeks.

index.html contains hashed bundle files, but without getting new index.html, new bundle files will never be pulled. Basically no javascript file is loaded from server, only some tracking scripts of third parties.

Now we cannot deploy backend changes because it would break pages of the app.

Is there any best practise for how long should we wait to release updates which would break app if user had index.html cached?

Or any other workarounds how to resolve problem above?