Tyr, Lathander, and Sune move against Cyric and successfully imprison the Black Sun in his Supreme Throne, under a sentence of house arrest to last one thousand years.
This is confirmed in the Forgotten Realms Campaign Guide (page 74) for D&D 4th edition:
Tyr, Lathander, and Sune united to imprison him in his nightmarish playhouse of a plane, the Supreme Throne, where he remains to this day, alone and increasingly insane.
I read to this day as the Year of the Ageless One, i.e. 1479 DR, as written in the same guide at the very beginning of the introduction via Elminster's words. The Sword Coast Adventurer's Guide sets the current year to 1489 DR; only 104 years has passed since Cyric was imprisoned. On page 27, there is only a little paragraph about Cyric and his church, without any details about his imprisonment.
I wonder what the consequences of Cyric's imprisonment on his church and worshippers are, since it seems there are none. Is Cyric actually free, and he can roam wherever he wants? Or is he still trapped in the Supreme Throne? Is his power diminished? Can he talk to / communicate with his worshippers?
Moreover, at page 45 of the Forgotten Realms Campaign Guide (among the examples for epic tier treasure) one can read
50,000 gp: A black iron key said to be one of the seven required to unlock Cyric’s shackles on the Supreme Throne.
Are there other references to these keys in official material (published books, manuals, adventures) or even tweets from Greenwood or other authors?
I am actually DMing a homebrew campaign and (theoretically) I can do whatever I want, but I prefer to be as faithful as possible to the official campaign setting.
If you have any details coming from current adventures (Princes of Apocalypse, Rise of Tiamat, etc.), please use the spoiler formatting.