  In this work, we carry out a suite of specially-designed numerical
simulations to shed further light on dark matter (DM) subhalo survival at mass
scales relevant for gamma-ray DM searches, a topic subject to intense debate
nowadays. Specifically, we have developed and employed an improved version of
DASH, a GPU $N$-body code, to study the evolution of low-mass subhaloes inside
a Milky Way-like halo with unprecedented accuracy, reaching solar-mass and
sub-parsec resolution in our simulations. We simulate subhaloes with varying
mass, concentration, and orbital properties, and consider the effect of the
gravitational potential of the Milky Way galaxy itself. More specifically, we
analyze the evolution of both the bound mass fraction and annihilation
luminosity of subhaloes, finding that most subhaloes survive until present
time, even though in some cases they lose more than 99% of their mass at
accretion. Baryons in the host induce a much more severe mass loss, especially
when the subhalo orbit is more parallel to the galactic disk. Many of these
subhaloes cross the solar galactocentric radius, thus making it easier to
detect their annihilation fluxes from Earth. We find subhaloes orbiting a
DM-only halo with a pericentre in the solar vicinity to lose 70-90% of their
initial annihilation luminosity at redshift zero, which increases up to 99%
when baryons are also included in the host. We find a strong relation between
subhalo's mass loss and the effective tidal field at pericentre. Indeed, much
of the dependence on concentration, orbital parameters, host potential and
baryonic components can be explained through this single parameter. In addition
to shedding light on the survival of low-mass galactic subhaloes, our results
can provide detailed predictions that will aid current and future quests for
the nature of DM.
