A new Rihanna song called 'A Night' has been registered and it would appear to involve Florence 'Florence' Welch in some capacity.
As you can see from the screengrab above (taken from the PJ forum), the song lists Florence and Paul Epworth as writers but, given its title, there's speculation the song just features a sample from Florence's 'Only If For A Night', rather than a full-blown 'feat'.
Who knows really. Who knows if Rihanna will ever release a note of music again. Who knows if she ever really existed in the first place?