Just set the inactive accounts so they are not included in Fetch All. Account-> Account settings-> Preferences-> turn off 'Include this account in Fetch All'.
In fact, dead accounts should not prevent live accounts from fetching, but over the years, a lot of duplicate operations were turned off, to prevent problems. Now that we have a programmer who is interested, some of that can probably be reversed, but it will take time to do it, and make sure that it doesn't cause problems.