The /etc/path_to_inst file is corrupted, I can't boot.

You will need to remove the file and then boot with -a and it will
ask you to rebuild the path_to_inst file. It is possible that you
still can't boot after that: if you've added/removed
controllers/disks, the numbering of the controllers may have
changed. You may need to find the new name of /usr and then edit
/etc/vfstab to change all the disk names.