According the QRH, for cat 2/3 approaches you need 1 standby attitude indicator. The "standard" is that any malfunction should be fixed before passing 1000 ft AAL. When this can't be done, a go around should be executed and a setup for another approach should be done. This either after fixing the problem, or taking into consideration the failed equipment.
Of course, if you know the weather is below cat 1 you might not have noticed the failure until you landed. This depends on how much you want to go home, how much you want to please your company to be "on time" etc.
Good airmanship would be the first option and perform a cat 1 landing (somewhere).