In your case it was the volume that ran out of space, because the deleted blocks on the host were not being released on the storage, that caused the LUN offline issue. We can ignore the LUN being 100% full, it was that the volume reaching 100% full that was the problem. Since the blocks were not deleted at the storage layer, only on the host OS, then as far as the volume is concerned it was full and could not accept anymore writes, so took the LUN offline to ensure no data loss. In every case you must monitor the usage of the volume.
A thick provisioned volume will only guarantee that the blocks have been reserved in the aggregate. A thick provisioned LUN only guarantees that it will have the blocks reserved in the volume rather than consumed by snapshots (not relevant in your case), but assuming the volume does not run out of space. If the volume is full, both a thick and thin provisioned LUN will go offline at the next write (or remain online but read only if space-alloc has been enabled).
If you do not over provision your aggregate, which in this case since its the only volume not a problem, then there is no disadvantage to using thin volume and thin LUN. You will benefit from automatic space reclaimation of deleted block by enabling the space-alloc LUN option, meaning the volume should not fill again due to a large deletion of the file system data. Also, all storage efficiency space savings will be realised in the volume/aggregate, meaning more available space in volume before it fills.
You will need to actively monitor the free space in the volume, however enabling volume autosize will assist here to automatically resize the volume if it is close to filling. Just remember a full volume is not good for a thick or thin LUN. Space reclaim in SnapDrive is a scheduled process on the server, while space-alloc (if thin provisioned) happens automatically on the storage. As mentioned, space-alloc also allows the LUN to remain online in the volume full scenario in a read only mode, rather than going offline.
Thanks,
Grant.