Regardless if they hit the water or solid ground the electronics would still be largely intact if you shoot them with 20 mm cannon the electronics will in a million pieces, again just reporting on what I read
A competent mission planner would have equipped the electronics with self-destruct charges. The Chinese could not have expected to recover their system and would not want it to be recovered by anybody else.
Other posters have already mentioned that shooting down a high-altitude balloon with bullets is a lot harder than it looks, and risks the aircraft on each pass.