  We explore the evolution of the different ejecta components generated during
the merger of a neutron star (NS) and a black hole (BH). Our focus is the
interplay between material ejected dynamically during the merger, and the wind
launched on a viscous timescale by the remnant accretion disk. These components
are expected to contribute to an electromagnetic transient and to produce
r-process elements, each with a different signature when considered separately.
Here we introduce a two-step approach to investigate their combined evolution,
using two- and three-dimensional hydrodynamic simulations. Starting from the
output of a merger simulation, we identify each component in the initial
condition based on its phase space distribution, and evolve the accretion disk
in axisymmetry. The wind blown from this disk is injected into a
three-dimensional computational domain where the dynamical ejecta is evolved.
We find that the wind can suppress fallback accretion on timescales longer than
~100 ms. Due to self-similar viscous evolution, the disk accretion at late
times nevertheless approaches a power-law time dependence $\propto t^{-2.2}$.
This can power some late-time GRB engine activity, although the available
energy is significantly less than in traditional fallback models. Inclusion of
radioactive heating due to the r-process does not significantly affect the
fallback accretion rate or the disk wind. We do not find any significant
modification to the wind properties at large radius due to interaction with the
dynamical ejecta. This is a consequence of the different expansion velocities
of the two components.
