You'd not break the ASI or the altimeter since those provide vital flight information and won't work after you've hit them with the fire extinguisher.
You'd not break the AI, since it's not connected to the pitot-static system.
So that leaves the VSI - which as it happens has an internal casing connected to static. So, by smashing it, you've turned it into a static port inside the cockpit, which will be at sort-of-ish ambient static.
As a result you'll get a reasonable approximation to static feeding the ASI and altimeter - good enough to get you home (to explain why you've just smashed up a perfectly good VSI).
G