have you ever thought that it simply means:
- ILS course? A/C course? are they the same? If so... then the A/C decrab algorithm will work... If not? well... it will not decrab normally, then maybe you should go with Max CAT II manual landing... or GO Around...
The FMGS is supposed to update your BIAS as soon as a LOC signal is caught, but even so, if you're on the LOC beam, with the correct ILS course set, but your real course is +7º, then I think your IRS just got busted in att mode.
Will you really continue APP for landing, flare and roll-out when something's not smelling right (lets say... with 150m visibility?)