You say you can hear the ignitor sparking, so the propane jet is the most likely problem. Maybe some rust or other debris clogged the nozzle. Poor propane flow or the ignitor too far away from the propane jet and it will not light. This problem could have been created when you removed the furnace to fix the blower problem. Another problem could be with the "sail switch", this keeps the propane valve shut off if the blower is not providing sufficient air flow for safe combustion. Slow blower speed, maybe due to low voltage, obstructions in the duct, or a sticking "sail switch" are all possible problems. And yes, the blower will run continuously waiting for the burner to fire up. Some furnace models do have a timer function to shut the fan off if the burner does not light after a few minutes.
Some yrs ago, I had an intermittent issue. At lower altitudes it worked all the time, but in the mountains it would turn on one time and next time just the blower would run. Propane diffused faster at high altitude and the ignitor needed to be located just right or it wouldn't light the propane every time.