The 1st part of your question
How do the companies that own these sats feel about this? Would they ever want their non-operational tech salvaged instead of burnt up in the atmosphere?
seems to imply that, after a company has lost control of a space object (dead satellites, rocket boosters,...) they are still entitled to claim ownership (because they paid for it). The answer is no, they can't. It is the state that registered the objects that has ownership of the object (well, if that state is a signatory or party of the Outer Space Treaty, Art VIII). Same goes for the counterpart, the liabilities (same reference, Art VII).
For the 2nd part of your question, you should know that the atmosphere extends very far into outer space Wiki. Satellites high-up to about 600Km can still "feel" the drag effect of atmospheric particles, thus reducing their lifetime. Without a repetitive altitude keeping engine, they inevitably fall back (and usually burn before they crash). Below ~350Km, they fall back fairly quickly (years if not months). Above ~700 Km they can continue to orbit for centuries. The bottom line is that although the size of the object plays a role in the drag, it is really the orbit height that is determining. So, "pushing an object into the atmosphere" means lower its orbit until the drag effect is strong enough to bring it down (hopefully quickly). This is why most launching states ask that satellite companies keep enough fuel at end-of-life to have a controlled re-entry (for low orbits) or to boost into higher orbits (for GEO).
For the Chinese booster (and other junks belonging to the US,Russia, France, ... as part of their expendable launches, and by -bad- design or by accident can't have controlled-reentry), had it not crash in the high seas, but say in Australia, what would happen on the legal side? If the crash creates damages to Australians lives and properties, it is the Chinese government who is liable (even if the booster belongs to a private company, say SinoX). If it doesn't, Australia MUST return all the debris to China, as per the Outer Space Treaty.
You may ask, if there is a dispute, say on the indemnifications, which tribunal has jurisdiction and can it enforce its decision? This is where the bat hurts ... the Treaty is silent on that.