The Cleric Clouds subdomain reads as follows:
Thundercloud (Su): At 8th level, you can, as a standard action, summon a storm cloud. This power functions as fog cloud except that creatures inside the cloud are deafened and take 2d6 points of electricity damage each round from the flashes of thunder and lightning. Once created, you can concentrate on the cloud to move it up to 30 feet each round. You can use this ability for a number of rounds per day equal to your cleric level. These rounds do not need to be consecutive.
It seems that this spell deals 2d6 of automatic area damage and deafens a creature with no save. It does not indicate a duration for the deafness.
It doesn't say the deafness is permanent and it does say "creatures inside the cloud are deafened" so I read that to mean the deafness lasts only while they remain in the cloud.
As for the no-save damage, that's how it's written. The general rule defines save DCs for when a sub-domain "calls for a saving throw". This one does not call for any save, so it seems that there is no save. So, if you can find a critter with low enough movement that you can kill it with 16d6 of electricity, just keep the cloud on it. Of course, almost anything can use a double move to get out of the cloud, so at best you keep them running instead of fighting.