My Ops Manual says:
"At flare height.
If FLARE does not come up on FMA, a go-around must be performed.
If visual references are sufficient and a manual landing is possible, the PF may decide to complete the landing."
Q. How does PM know that PF has sufficient visual reference to complete the landing or not?
PM should normally hear, "50, Flare, 30, 20, 10, Retard".
If PF only hears "50 ... 30, 20" etc. then that should be sufficient to realise PM has not called "Flare" and then take the appropriate action.