If a company have arranged things so their work can't enter the public domain (eg DRM) then they should not get copyright protection, fundamentally it's wrong to get the benefit of copyright without giving up your work to the public domain.
This can be solved by a requirement to register an unhindered copy, whilst they're at it orphaned works should be made copyright free, IMO.
Besides, we'd have to have copyright periods on software of 3-5 years, 10 tops, for software copyright to even make sense. Not 70+, which is longer than any recognizable computer industry ever existed.
This arrangement would also protect the public good in cases where the original company has gone bankrupt, or where the source code would otherwise have been lost.
If they never release the source code at all, I think we're just screwed, legally anyway. The DRM was attached to your binary or stream (or book), not the original source material. We may not like it, but I don't think it's copyright you have to worry about when it comes to closed source code.
In my ideal world, if the source code is not placed under escrow and tested to result in the distributed binary, then there would be no monopoly given to that binary. Anybody is allowed to copy it to the fullest extent that they are able to.