  The diffuse supernova neutrino background (DSNB) is the constant flux of
neutrinos and antineutrinos emitted by all past core collapses in the
observable Universe. We study the potential to extract information on the
neutrino lifetime from the upcoming observation of the DSNB flux. The DSNB flux
has a unique sensitivity to neutrino nonradiative decay for $\tau / m \in
\left[ 10^9, 10^{11}\right]$~s/eV. To this end, we integrate, for the first
time, astrophysical uncertainties, the contribution from failed supernovae, and
a three-neutrino description of neutrino nonradiative decay. We present our
predictions for future detection at the running Super-Kamiokande + Gd and the
upcoming Hyper-Kamiokande, JUNO, and DUNE experiments. Finally, our results
show the importance of identifying the neutrino mass ordering to restrict the
possible decay scenarios for the impact of nonradiative neutrino decay on the
DSNB.
