An alternative to death counters would be making a similar type of counter by creating lots and lots of burrowed units.. once there are X amount of burrowed units (lets just use 100 for an example), then remove all the units, start the music again, and start the spawning again. If this creates a problem with the map unit limit, you could do something where it spawns a zling on a counter, but replace a hydralisk for every 10 zlings, and then reset once there are 10 hydras.
If you have used every death counter, score counter, ore, gas, AND have no room for a 1x1 spawning locatin on your map or there are lots of units, then you could actually do a LONG chain of switch combinations, but that would take forever because you would have to make a trigger per tick. If you have used every switch... well, then I'm just out of ideas
