No experience with AIX myself, but here's what I came up with.
Found the AIX LVM manual for free download on the IBM website.
- Part of the HD that failed was a member of the other VG, though I would imagine you would still see the other PVs as members of the VG, but the VG would be incomplete. Might look into some of the lspv switches to get more information.
- The other VG isn't being activated so its LVs aren't being mapped to the /dev filesystem. Try activating the other VG. Maybe the rootvg you restored isn't configured to scan automatically for other VGs?
- Your other VG is hosed, so something more significant happened than just one drive failing. Have you done any postmortem analysis of the failed disk?