Most departments in this area are overwhelmed with cases, with not enough detectives to go around. My husband is a former detective, and I remember him talking frequently about frustrating cases in which leads were drying up, or where the evidence was pointing to no actual crime having been committed (e.g. in the case of someone who ran away). He hated to back burner cases, but with so many other active cases to tend to, he couldn't devote all of his energy to such cases. They would stay on his mind though, and I know he'd always be on the lookout for something new (especially if another case he worked on wound up creating a lead for the cold case).
With the limited information we have, I do believe as well that he left voluntarily. We know he deceived his wife into thinking he was going to a meeting, and then hopped on BART (with his hat and glasses case hidden in his folder that "should" have contained paperwork). He researched in advance a route for that day's trip. And he's seen in two photos, hours apart, in locations indicated by those internet searches, and he was alone. Nothing points to foul play, from what we've seen. And given his immense legal/financial troubles, it would make a lot of sense that he might think disappearing (and/or committing suicide) would lift the burden not just for him but for his family. I know that the proceedings will continue anyway... but when you've reached such a breaking point, emotion can very easily trump logic, even for the smartest people (my dad also committed suicide, so I've witnessed this with him).
My fear is that John intended to end his life. The area he visited is known for such things. Even the Lands End Labyrinth, where someone claims they spotted him that afternoon, has seen such activity. A person's body, once in the ocean, can easily be carried away/under, never to be seen again (or it could be weeks/months before it resurfaces).
That said, until he's found -- in any condition -- it's great for people to keep an eye out for him in case he decided to just purely run away. The PD may have exhausted all of the leads up to now. But the family can certainly keep the search alive in the hopes that a new promising lead will materialize, that would give the PD something to work with.
I hope answers are just around the corner for the family, and that John is brought home to them soon.
). 
I think it's more wait and see what the family wants to do next. It's a lull and it's quiet but we're still here.
