Realistically, even without "shall," most states carry the legal obligation in state statutes not the state constitution. The problem is that the crime is minor and will almost certainly be pardoned immediately by Trump. So even if it's "illegal," oh well. The governor refuses to certify, thereby breaking the law, Johnson still holds the deadline, the number of EC votes is lowered, Trump is declared the winner, and then the governors are pardoned and are in the good graces of the incoming POTUS.
Just to be clear, that makes everything valid and constitutional at the federal level for this plan. I don't think you're grasping how fully fucked we might be.
The VP certifies the results received by the deadline. That wouldn't change anything here, and she would be obligated to declare Trump the winner. Like Pence, the VP can't decide not to certify legitimate results submitted to congress by the deadline. The point here is that select blue states won't make the deadline through republican stalling, SCOTUS won't "interfere" in the election by adjudication, so the VP is required to only consider the full electors submitted by the deadline. And it would be perfectly valid at the federal level. The state actors might be committing a crime by stalling, but Trump will pardon them, so they really have little risk.