Clients do not access shared resources when the domain controller is unavailable

[Aeper_-_Andrea]

Good morning,
I need help to solve this problem.
My network structure is composed of a DC (maindc) and 3 other servers located on different sites.
The client PCs access the shared resources from the site where they are located.
When the DC is not available it happens that the client PCs do not reach the shared resources (distributed printers, shared folders).
Does anyone have any idea how I can solve this problem?
Thank you for your help

[#2]

where would all of the clients be resolving the names of the shared resources? Perhaps via the DC?