I do have some experience with this “law and facts” issue in the real world.
My experience is that if a prosecutor is very determined to pursue a case, and is willing to commit the necessary resources to get it done, they can find the appropriate legal framework to match the relevant facts and will be able to convince a grand jury to get an indictment. (Conviction, of course, may be more difficult.)
If they are lukewarm or are not that interested in the case (for whatever reason) they can easily decide not to pursue it.
FISA abuse is a _big_ deal, and this should be a very high priority case.
Failure to pursue it is indicative of a lack of will, imho, and is not a function of either the law or the facts.
It's the top of the iceberg. Read Collyer's April 2017 Opinion and Order. The government undetakes RAMPANT warrantless snooping -- which is coincidentally constitiutional when performed to gather foreign intelligence.
The FISA warrant stack is there to "prove" a falsehood - that the government uses utmost care and the highest standards before snooping.
I see a real practical barrier to getting a "lied to the FISA court" conviction. I bet the application is literally true. Misleading, but literally true.