Better handling of dead sources

Describe your suggested feature

Server should handle dead sources better.

It is just a sad fact of life that manga websites die from time to time, some earlier, some later. When that happens suwayomi users have a choice: remove the obsolete source or keep it. Both choices currently suck:

1. Keeping the source means it gets pinged when searching for mangas delaying results for no reason. Also makes the update operations slow, keeps junk entries in browse page etc.
2. Removing the source makes the already downloaded manga inacessible. Files are on disk but server refuses to display them with error:

I think there should be a better way to handle dead sources: mark them as read-only or something else to avoid the above issues.

Other details

Error is from server v2.3.2298

Acknowledgements

• I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open or closed issue.
• I have written a short but informative title (ideally less than ~100 characters).
• I have updated the (Suwayomi-WebUI and Suwayomi-Server) to the latest versions
• I have filled out all of the requested information in this form, including specific version numbers.