No, Marco's still with Nightwish. The article saying that he left was an April Fool's joke in 2010.
Look up Showtime, Storytime on Youtube. It's live recordings of some of Nightwish's stuff with their new singer, but they haven't had original content with her yet.
I've heard of Therion, I just don't like them. I'm more a fan of Epica.
I haven't found any good Christian symphonic metal bands. They just don't exist. Some say they are symphonic metal but are in fact, not. Like Divinefire. There is HB (stands for Holy Bible) but they are Finnish, and only have one song in the English language. They have been accused of not being Christian because while their lead singer doesn't bare any cleavage, midriff, or leg her clothing is still fairly tight.
Look up Showtime, Storytime on Youtube. It's live recordings of some of Nightwish's stuff with their new singer, but they haven't had original content with her yet.