^^ Not much of a chance. The valve doesn't hang below the plastic belly pan. I suppose someone who does off-roading with a Subaru might have reason to be concerned, but the Impreza isn't an off-roading car, so that shouldn't be much of a concern. If you break the Fumoto valve off your oil pan, you've probably done other damage to your car too (exhaust and more).
My oil change with the valve was much less messy than my first oil change using the drain plug. 0W-20 oil is super thin (especially when it's hot), and with the drain plug it dumps out of your oil pan FAST. I don't care how you position your catch pan, you're going to splash some oil. The Fumoto valve with the nipple (F-108N, I believe) and hose gives much better control of where the oil goes.