So what your trying to pull is if all the the Necron tomb worlds are up then they will win...
SOOOOO lets point some things out:
Very few and very tiny things can phase out of existance, not everything in the Necrons can do this, in fact very little can.
Hive Mind vs Necrons = Hive Mind winning, Necrons might be technical and somewhat "together" but they still have A LOT of infighting between Lords, Overlords, and Phearons. The Hive Mind is ALL TYRANIDS together and is barely even waking up now. Along with the fact that the Tyranids are indeed much better at combating opponants then Necrons, the whole calculating their next move thing does not happen. Just because they are machines does not mean they are all knowing.
One or maximum 3 Hive Fleets... How big do think the Tyranids are?
Also, Living things need amounts of metals in them as well, Necrons are not useless :) and their adaptation will not stop because of little biomass.
As for leading them to a planet with the Black Spires if someone would care to give me rough draft on them I would like that because i'm not familiar with what those are.
Also they can't do large scale stasis tricks.