  In the last stages of a black hole merger, the binary can experience a recoil
due to asymmetric emission of gravitational radiation. Recent numerical
relativity simulations suggest that the recoil velocity can be as high as a few
thousands kilometers per second for particular configurations. We consider here
the effect of a worst case scenario for orbital and phase configurations on the
hierarchical evolution of the massive black hole (MBH) population. The orbital
configuration and spin orientation in the plane is chosen to be the one
yielding the highest possible kick. Masses and spin magnitudes are instead
derived self-consistently from the MBH evolutionary models. If seeds form
early, e.g. as remnants of the first stars, almost the totality of the first
few generation of binaries are ejected. The fraction of lost binaries decreases
at later times due to a combination of the binary mass ratio distribution
becoming shallower, and the deepening of the hosts potential wells. If seeds
form at later times, in more massive halos, the retention rate is much higher.
We show that the gravitational recoil does not pose a threat to the evolution
of the MBH population that we observe locally in either case, although high
mass seeds seem to be favored. The gravitational recoil is instead a real
hazard for (i) MBHs in biased halos at high-redshift, where mergers are more
common, and the potential wells still relatively shallow. Similarly, it is very
challenging to retain (ii) MBHs merging in star clusters.
