As much as people ***** about lawsuits, this is a good example of the level of negligence you have to prove to actually win one in a recreational pursuit setting.
The court in this case explicitly recognized a complete bar to recovery where a plaintiff has reasonably chosen to bear the risk of a particular harm. They give the example of someone getting hit by a stray ball at a baseball game. In our terms, they would have barred recovery from any harm that resulted from a true recreational dive.
However, in this case, the dive charter exceeded all safety standards for a recreational dive, so there was no bar to recovery. At this point it becomes a question of contributory negligence, i.e. how much each party was at fault.
Back to the buddy situation. This case was about the charter's liability, any speculations on the responsibility of buddies to each other (as opposed to the responsibility of the charter to assign buddies) have no legal force. Note that this decision actually would protect the dive charter from those who intentionally plan on diving solo, since solo divers choose to bear certain risks and thus would be barred from recovering from an injury arising out of those risks. At worst this decision would require charters to at least offer everyone a chance to buddy up, and presumably to assign a DM to an odd man/woman out who wanted a buddy. All the boats I've been on do this anyway - so what's the harm here?