So it can restore without a backup? And also can I use someone else's backup for my wii, patch or something?
yes it is possible to restore a nand backup from another wii.
Not without some work though. You also would need the keys from your Wii as well or you can't change the other persons backup to work for your Wii.
What was meant by still being able to fix a brick as long as you at least have bootmii installed as boot2, is that if you get bricked, you should still be able to access the HBC from bootmii or at least a wad manager with cboot2 and using that you can likely fix whatever it is you did to mess your Wii up. A NAND restore is pretty much just an easy way out to just go back in time to before you fucked up, but in doing it you will lose EVERYTHING done between the time you made the backup and the time you restored it, which is why periodic backups are suggested or at least fresh ones before you do any new installations of anything.
Also, it's highly unlikely that installing a cIOS alone will brick your Wii. A brick is generally caused by messing with something to do with the boot process/system menu and mostly a user doing something really stupid like uninstalling their system menu IOS or even the system menu itself. A slightly less user faulted way of bricking is installing a wad of some channel with a badly formed banner which will cause a banner brick. For those types of bricks, even if you can't install bootmii to boot2 on your Wii, pre/priiloader is enough to fix a banner brick (though boot2 bootmii can as well). To fix that all you need to do is load the HBC/wad manager from preloader or bootmii and then just uninstall the bad wad that caused it (Don't apply this fix to IOS wad's though, especially system menu IOS wad's.)