Ouch amigo...
The temp drop is not a 'good' thing, but I would be more worried about the lack of flow and oxygenation for such a prolonged period of time. That really takes a toll on corals and other reef inhabitants. In the ocean, there are thermals that pass through where temp drops are very sudden - corals and the lot can handle temp changes, but they are never without water flow in their natural habitats.
I am sorry either way dude.
The only thing you can do now is bring things slowly back up to par and hope for the best. If you see things obviously not going to make it - take it out before it dies and pollutes the water even more. If your water becomes (or is) toxic (ammonia spike - e.g. crash), fix that ASAP or it will cause even more damage.