I'm frequently wrong, and haven't looked at the books for a hundred years, but the TAC operates with an engine failure in the cruise unless it's lost engine data, in which case you will probably get it back after running the cx list and resetting the TAC switch to re-initialise the system.
You will lose rudder control on a go-round (TAC off) when you select a lateral mode because the a/p had been trimming the rudder for the autoland. TAC on, it will still function and won't be a problem and you shouldn't have to use the foot rests.