  Some binary systems composed of a white dwarf (WD) and a hot subdwarf (sdB)
helium star will make contact within the helium burning lifetime of the sdB
star. The accreted helium on the WD inevitably undergoes a thermonuclear
instability, causing a detonation that is expected to transition into the WD
core and lead to a thermonuclear supernova while the donor orbits nearby with
high velocity. Motivated by the recent discovery of fast-moving objects that
occupy unusual locations on the HR diagram, we explore the impact of the
thermonuclear supernovae on the donors in this specific double detonation
scenario. We use MESA to model the binary up to the moment of detonation, then
3D Athena++ to model the hydrodynamic interaction of the supernova ejecta with
the donor star, calculating the amount of mass that is stripped and the entropy
deposited in the deep stellar interior by the strong shock that traverses it.
We show that these donor remnants are ejected with velocities primarily set by
their orbital speeds: $700-900\ \rm km\ s^{-1}$. We model the long-term thermal
evolution of remnants by introducing the shock entropy into MESA models. In
response to this entropy change, donor remnants expand and brighten for
timescales ranging from $10^6-10^8$ years, giving ample time for these runaway
stars to be observed in their inflated state before they leave the galaxy. Even
after surface layers are stripped, some donors retain enough mass to resume
core helium burning and further delay fading for more than $10^8$ years.
