^if the coolant return is working properly, the coolant that has been purged into the overflow tank will be siphoned back into the radiator. As tortron has pointed out, the radiator no longer has air flow or coolant passing through it and the coolant in the block will begin to heat soak. If it passes a coolant test I would say the chances of a crack in the head, block or a failed gasket are very slim.

*don't ever check your coolant while the engine is hot. If you are desperate and need to drop engine temps quickly, pour water over the radiator slowly. This will intracool the system at a rate that won't crack the head or block and bring engine temps to below normal operating temperatures.