I guess alert height depends. Now on the A320 we use 100ft, on the 737NG with their newer fail operational system it used to be 200ft, although the alert height does not mean that no failures can happen, it means that single failures below alert height will still lead to a successful autoland. Never had any failures in real live, but at least in the SIM the 737 could cope with pretty much every single failure after 200ft, including complete loss of ILS signal and a wind shift from one side max crosswind to the other side max crosswind, not to mention the easy stuff of course like loss of engine/generator etc.
To be honest, losing automatic rollout with just 75m RVR would be very scary indeed, especially in the high speed portion of the rollout. I had to operate a few times in those visibilities, and just normal taxying basically slowed down to a 5kt crawl because everything else was just not possible.