First thing you want to do is shut down the VC ports. Then recycle the FPC number for the switch you want to revert to standalone. Then connect the console port and load the factory default on that switch.
You can also drop the shell and delete the vc* files
root@sw1:RE:0% cd /config
root@sw1:RE:0% ls vchassis/
vc.db vc.param vc.tlv.db vc.tlv.db.0 vc.tlv.db.1
root@sw1:RE:0% rm vc*
rm: vchassis: is a directory
root@sw1:RE:0% rm vchassis/*