Her Beloved is Bahamut, the non primal one that we have never seen outside artwork, we could guess Primal Bahamut might be a 1 for 1 but we can't say for certain at this point.
Tiamat is remaining put unless someone forces her out, her mindset is set in stone that she needs to eternally repent for summoning Primal Bahamut in her grief, there is no way anyone can convince her given how long she has put herself through what she has.
If Tiamat returns, it is by force, she will not leave her 'captivity' willingly, an act like that is not something we traditionally do more like a villain thing especially when we have just left her there for 2 wars and a shard world hopping.
