Had a flame angel die on me and i believe it took out my cardinals as well. To this day im not sure what got him.
I put a pair of clowns, then a hawkfish, then a bi color angel in the tank and that time the angel faired better. I would love another flame angel, but i dont have 90$ to throw away on something ive managed kill once already.
I used a used tank for them, and it may have been old copper treatment, or bacteria that managed to survive from the freshwater set up. Or it could be as sarah mentioned, shipping. Mine took a 5 hour bus trip to me, and 5 hours on a bus is enough to stress anyone.
Edit: Also what are your water params?