  We present $\textit{Hubble Space Telescope}$ imaging of the Calcium-rich
supernova (SN) 2019ehk at 276 - 389 days after explosion. These observations
represent the latest photometric measurements of a Calcium-rich transient to
date and allows for the first opportunity to analyze the late-time evolution of
an object in this observational SN class. We find that the late-time bolometric
light curve of SN 2019ehk can be described predominantly through the
radioactive decay of ${}^{56}\textrm{Co}$ for which we derive a mass of
$M({}^{56}\textrm{Co}) = (2.8 \pm 0.1) \times 10^{-2}$$\rm{M}_\odot$.
Furthermore, the rate of decline in bolometric luminosity requires the leakage
of $\gamma$-rays on timescale $t_{\gamma} = 53.9 \pm 1.30$ days, but we find no
statistical evidence for incomplete positron trapping in the SN ejecta. While
our observations cannot constrain the exact masses of other radioactive
isotopes synthesized in SN 2019ehk, we estimate a mass ratio limit of
$M({}^{57}\textrm{Co}) / M({}^{56}\textrm{Co}) \leq 0.030$. This limit is
consistent with the explosive nucleosynthesis produced in the merger of
low-mass white dwarfs, which is one of the favored progenitor scenarios in
early-time studies of SN 2019ehk.
