  We present the final sample of 98 detached double white dwarf (WD) binaries
found in the Extremely Low Mass (ELM) Survey, a spectroscopic survey targeting
<0.3 Msun He-core WDs completed in the Sloan Digital Sky Survey footprint. Over
the course of the survey we observed ancillary low mass WD candidates like
GD278, which we show is a P=0.19 d double WD binary, as well as candidates that
turn out to be field blue straggler/subdwarf A-type stars with luminosities too
large to be WDs given their Gaia parallaxes. Here, we define a clean sample of
ELM WDs that is complete within our target selection and magnitude range
15<g_0<20 mag. The measurements are consistent with 100% of ELM WDs being
0.0089 < P < 1.5 d double WD binaries, 35% of which belong to the Galactic
halo. We infer these are mostly He+CO WD binaries given the measurement
constraints. The merger rate of the observed He+CO WD binaries exceeds the
formation rate of stable mass transfer AM CVn binaries by a factor of 25, and
so the majority of He+CO WD binaries must experience unstable mass transfer and
merge. The shortest-period systems like J0651+2844 are signature {\it LISA}
verification binaries that can be studied with gravitational waves and light.
