  The Type IIn supernova (SN) 2005ip is one of the most well-studied and
long-lasting examples of a SN interacting with its circumstellar environment.
The optical light curve plateaued at a nearly constant level for more than five
years, suggesting ongoing shock interaction with an extended and clumpy
circumstellar medium (CSM). Here we present continued observations of the SN
from $\sim 1000-5000$ days post-explosion at all wavelengths, including X-ray,
ultraviolet, near-infrared, and mid-infrared. The UV spectra probe the
pre-explosion mass loss and show evidence for CNO processing. From the
bolometric light curve, we find that the total radiated energy is in excess of
$10^{50}$ erg, the progenitor star's pre-explosion mass-loss rate was $\gtrsim
1 \times 10^{-2}\,{\rm M_{\odot}~ yr}^{-1}$, and the total mass lost shortly
before explosion was $\gtrsim 1\,{\rm M_\odot}$, though the mass lost could
have been considerably larger depending on the efficiency for the conversion of
kinetic energy to radiation. The ultraviolet through near-infrared spectrum is
characterised by two high density components, one with narrow high-ionisation
lines, and one with broader low-ionisation H I, He I, [O I], Mg II, and Fe II
lines. The rich Fe II spectrum is strongly affected by Ly$\alpha$ fluorescence,
consistent with spectral modeling. Both the Balmer and He I lines indicate a
decreasing CSM density during the late interaction period. We find similarities
to SN 1988Z, which shows a comparable change in spectrum at around the same
time during its very slow decline. These results suggest that, at long last,
the shock interaction in SN 2005ip may finally be on the decline.
