I missed the obvious suspect for severing Rozemyne's and Ferdinand's threads: Erwärmen. He was Liebeskhilfe's predecessor and has plenty of reason to begrudge Ferdinand and some to begrudge Rozemyne, not to mention that unlike the other gods, he can't tell the two apart anyway, while Rozemyne is dyed in his colour, i.e. once the divine mana was out of her system. So we have someone with the motive, the means and the demeanour. Mestionora was very against violence, while Erwärmen already tried to kill Ferdinand at least once, but failed thanks to Rozemyne's interference and didn't re-attempt it directly, almost asuredly because of Mestionora's decree banning all further killings.
Anyway, I'm off to read the freshly released pre-pub part now.