Kelsingra's silver and Verity's Skill river questions

[Nedcase]

It's a very good question and it still never truly got answered: Where did Verity's Skill River go in the last book (AF).  We know it went underground, but still . . why can't the dragons get to it somehow?  I think they probably will but Robin Hobb hasn't written that book yet.  That's how all the liveships will turn into dragons, when they find this underground river and drink their fill.  

There's SO much we never really find out that needs it's own trilogy after the Fitz and the Fool trilogy.  I don't want to put any spoilers in here so I won't voice my thoughts on this.  I really ought to start my own thread about it at some point.

I assumed the river was either a) in a different, as yet undiscovered city or b) in a different timeline, and that the pillars can transport over time as well as distance.