  Massive black hole binaries are expected to provide the strongest
gravitational wave signals for the Laser Interferometer Space Antenna (LISA), a
space mission targeting $\sim\,$mHz frequencies. As a result of the
technological challenges inherent in the mission's design, implementation and
long duration (4 yr nominal), the LISA data stream is expected to be affected
by relatively long gaps where no data is collected (either because of hardware
failures, or because of scheduled maintenance operations, such as re-pointing
of the antennas toward the Earth). Depending on their mass, massive black hole
binary signals may range from quasi-transient to very long lived, and it is
unclear how data gaps will impact detection and parameter estimation of these
sources. Here, we will explore this question by using state-of-the-art
astrophysical models for the population of massive black hole binaries, and by
investigating how many sources would be detected by LISA, with and without data
gaps. We will also assess the effect of the gaps on parameter estimation for
these sources, using the Fisher Information Matrix formalism as well as full
Bayesian analyses. Overall, we find that the effect of data gaps due to regular
maintenance of the spacecraft is negligible, except for systems that coalesce
within such a gap. The effect of unscheduled gaps, however, will probably be
more significant than that of scheduled ones.
