  We present the results from an extensive follow-up campaign of the Tidal
Disruption Event (TDE) ASASSN-15oi spanning $\delta t \sim 10 - 3000$ d,
offering an unprecedented window into the multiwavelength properties of a TDE
during its first $\approx 8$ years of evolution. ASASSN-15oi is one of the few
TDEs with strong detections at X-ray, optical/UV, and radio wavelengths and
featured two delayed radio flares at $\delta t \sim 180$ d and $\delta t \sim
1400$ d. Our observations at $> 1400$ d reveal an absence of thermal X-rays, a
late-time variability in the non-thermal X-ray emission, and sharp declines in
the non-thermal X-ray and radio emission at $\delta t \sim 2800$ d and $\sim
3000$ d, respectively. The UV emission shows no significant evolution at $>400$
d and remains above the pre-TDE level. We show that a cooling envelope model
can explain the thermal emission consistently across all epochs. We also find
that a scenario involving episodic ejection of material due to stream-stream
collisions is conducive to explaining the first radio flare. Given the peculiar
spectral and temporal evolution of the late-time emission, however,
constraining the origins of the second radio flare and the non-thermal X-rays
remains challenging. Our study underscores the critical role of long-term,
multiwavelength follow-up.
