  Dwarf spheroidal galaxies are dark matter dominated systems, and as such,
ideal for indirect dark matter searches. If dark matter decays into high-energy
photons in the dwarf galaxies, they will be a good target for current and
future generations of X-ray and gamma-ray telescopes. By adopting the latest
estimates of density profiles of dwarf galaxies in the Milky Way, we revise the
estimates dark matter decay rates in dwarf galaxies; our results are more
robust, but weaker than previous estimates. Applying these results, we study
the detectability of dark matter decays with X-ray and very-high-energy
gamma-ray telescopes, such as eROSITA, XRISM, Athena, HAWC, and CTA. Our
projection shows that all of these X-ray telescopes will be able to critically
assess the claim of the 7 keV sterile neutrino decays from stacked galaxy
clusters and nearby galaxies. For TeV decaying dark matter, we can constrain
its lifetime to be longer than $\sim$10$^{27}$-10$^{28}$ s. We also make
projections for future dwarf galaxies that would be newly discovered with the
Vera Rubin Observatory Legacy Survey of Space and Time, which will further
improve the expected sensitivity to dark matter decays both in the keV and PeV
mass ranges.
