..... you wont get any cold water running back up the hot pipe and spilling onto the floor .....
Water
will run out of the hot inlet if both taps are opened - difficult to avoid with some designs.
Kitchen sink mixers usually keep the flows seperate, basin mixers usually mix in the body of the tap.
Easy to fit a stop end to the redundant tail to seal it.
If you can find a single tap that will cover the hole, I would pack the gap with something like a couple of short bits of waste pipe with segments cut out lengthwise to telescope inside each other to centralise it. A 3/4" top hat washer may be useful too.