one way would be to keep a count of the number of blocks and deduct 1 each time 1 gets destroyed.
This isn´t false but remember you actually have an expression for this so no need to keep track of it yourself.
Block destroyed & block.count <= 1 --> go next layout
Iirc you compare to one because the block actually gets destroyed at the end of the tick so the comparison has to be true for 1 (but I might be wrong here, try it out)