There are only 2 possible bypass routes, both start at Berwick Bassett. One aims to join up with the A4 at the sanctuary the other goes behind Windmill hill passed Julians house and joins the A4 on the Calne road.
Neither of these will ever happen because of the huge amount of archaeology they would destroy.
Traffic damaging the stones, Na.
I've seen cars hit the Swindon stone at 60 miles and harldy even scratch the stone but totaled the car.
PeteG