From the (our) FCOM (PRO NOR SOP Management of degraded guidance)
"...the approach may be continued only if the following is completed prior to 1000 ft AAL:
ECAM completed
Approach procedure & minima briefed
Approach capability correct for new category of Approach
RVR acceptable for new Approach
New DH Entered
Decision to downgrade is made"
So if the RVR is below below minima, you're going around.
If below 1000 ft AAL, a downgrade (click click click...) is a go around unless you have & can maintain visual reference.