I would like to set up a DHCP-server with 3 DHCP-relays. Is there any way to make this failsafe so if the relays can't talk to the server they can still give out IP-addresses if needed? My other option is to set up four DHCP-servers but then I have four configs to update.
If you have multiple configs of anything to update, you should probably look at using puppet for configuration management and distribution.
Coupled with a good VCS, such as svn or bzr, it's one of the best way to keep configurations equal across multiple servers.