I think Cyric will be gone or, perhaps more accurately, the effects of his imprisonment will be increased so he no longer has any ability to grant spells or influence Toril. That would still leave him as a poor man's Tharizdun waiting to be released from his prison.
One of the reasons I think this will happen is that Elminster's Guide to the Forgotten Realms reduced its description of Cyric to about a paragraph unlike most of the other deities that it mentioned. I think if Cyric was going to play a larger role in the post- Sundering Realms he would have gotten a full write-up like Bane et al.