A_F - if the 'autoland warning' means the a/c is unable to complete an A/P landing, then in all the operators I have been with (737 all types) it is a mandatory g/a. The danger is that although there may be some visual clues at failure, they can rapidly disappear meaning that the flare and t/down could be endangered. I guess that if, in the unlikely event that it is CatIII for cloudbase and not visibility, you 'broke cloud' at 50'(/DH) and saw the whole runway you might be justified in going against the QRH (g/a) but I suspect there will a 'chat' in your manager's office!