Patching wouldn't work. Destructible terrain would become part of the gameplay, and you can't just patch gameplay issues for one side of the people and not the other side.
That said, why would one need PhsyX? Destructible terrain has been around far before PhysX ever existed. Hell, one of the first games that had a good degree of terrain destruction was Red Faction, a game released on the PS2 (mind you that the PS2 has a measly 300mhz processor). Even now, there are stand alone games that allow for completely changeable terrain without using something like PhysX.
http://www.youtube.com/watch?v=N30GvYz7MXk Miner Wars doesn't use PhysX at all, but allows you to 'dig' tunnels through asteroids (and no, they aren't pre-determined tunnels, they are completely 'customizable') or even blow entire parts of an asteroid (again, not pre-determined, you choose what you want to blow off)
PhysX just allowed for more complex calculations without needing a really powerful CPU. Before PhysX was around, physics calculations were mostly done by the CPU and weren't that intensive. Just have less physics going on, something exploding doesn't need to burst in a million pieces, a dozen pieces could be enough. 95% of todays games don't even use PhysX: Crysis, Half Life 2 both contain
VERY advanced physics systems, both don't use PhysX to calculate it.
Even if you MUST use PhysX, when ATI people would still be able to get a standalone PhysX card (if they are still being sold? Or did nVidia buy the entire company?). Though I think you could perfectly make a believable destruction of terrain without using PhysX at all. Just be careful with the amount of debris you create when letting something be destructed. A glass window pane, being destroyed and falling apart in 5 smaller pieces looks somewhat believable (more so than no destruction at all), but wouldn't tax your system that much.
@DT: Though I normally would agree with you that nVidia is far superior to ATI. I can't say I currently agree. ATI has always been the winner in the price/performance ratio, being much cheaper (though, in general, nVidia has always been the more powerful card at a much higher price), ATI's current flagship is more powerful than nVidia's (not too sure though, has the 480 already been released?) and ATI was the first to release a card with DX11.