check if the LUN is getting detected as a snapshot if so then we could try and mount it back.Because I have seen a simliar situation occur where it was getting detected as a snapshot volume.
run this command
esxcfg-volume -l
If you get an output like this
VMFS3 UUID/label: 49d22e2e-996a0dea-b555-001f2960aed8/VMFS_1
Can mount: Yes
Can resignature: Yes
Extent name: naa.60a98000503349394f3450667a744245
Then you can mount it using the command.
esxcfg-volume -m VMFS_UUID|label