It's a bigger game than that.

If they refuse an extension then we just revoke article 50

The SNP are wrong here about an extension followed by an election.
We need a new caretaker PM followed by a new referendum.

It should be clean break/no deal V Remain

It's the only thing that should calm all sides (as far as is possible)
With the caretaker PM enacting the result of the referendum them immediately calling an election.