Given that Attachmate have said they'll continue developing mono , surely they'll have wanted any IP rights that came with that, which would include any mono patents? The "certain intellectual property assets" sold to the (MS-controlled) CPTN Holdings LLC would surely be things not directly attached to any product, like the Unix copyrights; since Attachmate would want those that directly pertain to anything they'd continue developing.
Besides, it's not like Microsoft doesn't already hold a ton of patents (on .NET) that directly apply to mono. How could a few more change anything? What assurances we have against Microsoft suing are based on things like the Community Promise, not a hope that they don't have enough relevant patents. (And the patents Novell donated to the Open Invention Network were, well, donated. They presumably can't be undonated).