In this first instance the main clause only stands alone if you omit (then).
But in the other example it clearly has a main clause. So would this be classed as an embedded main clause as it only works as a independent clause if it's adjusted and or if it's joined with a dependent clause.
If I have enough money, then I will buy a new car.
If it rains, the picnic will be cancelled.
The picnic will be cancelled if it rains.