I think it was 33% for a weekend sale when the second DLC came out, so way back long before the summer sale.
No, it won't.
I got the game through Amazon recently and have been playing it using Origin. Origin is good and works well. Yeah, it's nice to have everything on Steam, but if you take that mindset, you'll miss out on some good deals elsewhere.
As it is, I don't believe Amalur has ever gone on sale on Steam.
On the subject of the currently new flash sales, Magicka and Hydrophobia are on 75% off at the same time!