They can finish the league if they like, but I reckon only fans of a few clubs will care. The problem is that form will go out of the window, because players will be lacking match fitness and tactical training, so the results will all be arbitrary.
You can argue (as many of the media have been) that Liverpool should be awarded the title, given that they are so far ahead, but what do you do about everything else? Promotion, relegation, Champions League, FA Cup, CL places etc. In the circumstances, the only equitable outcome is to declare everything null and void and start again when it's safe to do so.