I am wondering about one question. I have a RouterOS router with dhcp server using Radius. When a known mac-address tries to connect, it gets good IP address from Radius database. If the MAC is unknown, it gets a dhcp lease from a pool defined on the router. It works fine.
But when Radius connection is not available (dhcp,error,warning,info,debug ether2: radius authentication failed for 00:22:15:E3:D8:5B: RADIUS server is not responding), I get no lease at all (169.254..). Is there any way for dhcp server on RouterOS to assign addresses from a pool when Radius server is not responding?
The requested configuration is possible only with scripts.
As the sequence for user authorization is the following,
- firstly, local DHCP database (/ip dhcp-server lease) is checked;
- then, RADIUS server is contacted.
It means, when RADIUS server is not responding, you can get address from local database. But when addresses are assigned from local database, no information is being sent to RADIUS server.
You can make script, which will ping RADIUS server and when it is not responding, enable DHCP authorization from local database.
Thanks for information and for the idea! 
I will try to write the script soon 
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I realize this is an old thread, but how did you get it to give an ip when the Mac is unknown?