Ken Livingstone getting elected will be a good thing because he will do some good things while in office. It will not transform the direction of national politics however. This government does not have a democratic mandate and does not need a second term to complete its mission.
This government's mission is to destroy all currently existing bases for working class resistance. It is doing three key things (1) curtailing working class access to higher education (2) destroying the public sector unions as an effective force (3) gerrymandering constituencies and destroying public housing simultaneously through social cleansing.
Two things can stop the government. One is the hacking enquiry, the other is massive civil unrest centred around strikes. We cannot bring the first to any conclusion, and the ruling class is not going to destroy the police, the mass media and the three main parties at a time like this. The second we can bring about.
If we don't, regardless of who wins any election, we will get another generation of right wing governments.