Instances can go down, disappear or be unresponsive due to many reasons.
Go to your account settings now and export your account settings!
This file contains your subscriptions, follows, profile settings etc. It’s very easy to start over on a new instance when you have your export file.
Back it up, export it, save it, repeat occasionally.
Actually it can. Cookies, local storage … but using that for backups would certainly be an idea I haven’t heard before.
Plus it’s going to be a lot lire work to extract that when the website that wrote to it is no longer accessible. Easier to just click the backup button and download a file.