I think you fundamentally misunderstand what's being written down to zero. The movie is being written down to zero, not all of these extended rights and IP you're talking about.
That's how a company can lose more money on a $10 million sale then deleting it. If you have to include more than $10 worth of IP or obligations with the sale is a negative return. Alternatively, selling a movie could cost you more than $10 million in losses on a different movie.
These are all legitimate reasons to destroy instead of sell it. Avoiding costs are fundamentally different than increased Revenue for the purpose of taxes, even if they're monetary value is the same. Cost avoidance is not taxable value creation.
I can save $20 in laundry fees by not shitting in my bed, but I don't pay taxes on the value I saved. This is for two reasons. First, I'm no richer off after not shitting in my bed then I was before. Second, the alternative is I would have to pay taxes on every second of every day I chose not to shit in my bed.
I don't think that any retained rights are being valued at zero, besides the distribution rights to a a movie that doesn't exist.
If they keep the rights to develop a script, for example, that would have some tiny residual value.
