How to restore non bootable mksysb image

Never use restbyname command in NIM server.
If you want to restore in client use below
tctl -f /dev/rmt0.1 rewind
tctl -f /dev/rmt0.1 fsf 3
restbyname -xqf /dev/rmt0.1

Removing duplicate default route

lsattr -El inet0 -> sees bad route
chdev -l inet0 -a delroute=
lsattr -El inet0 -> bad routes removed