This is standard now. My REC Alpha Pure Black 400 panels are warrantied for 92% at 25 years.

The degradation is about 0.25%/yr. Assuming no exponential drop-off it would take >50 years to hit 80%.

Essentially no one has had to replace their panels due to degradation losses as of yet (since the vast majority of panels have been installed in the past ~30 years).

Generally you can find the degradation curve in their datasheet, and yes, 80% after 25 years sounds possible. IIRC they fade faster with time, so it might be 50% after 50, but ... that's still pretty good.

I don't see anything in the NREL data that suggests panel degradation accelerates. Most of the panels in their data have higher initial degradation, then less in subsequent years. This LG panel seems to be getting stronger as it ages: https://www.nrel.gov/docs/fy22osti/81172.pdf#page=28

you'll need to supplement with some new panels to account for the loss, but each new panel is more efficient than the one you're "replacing"

The idea that PV panels become trash in a decade is a lie promulgated by oil companies. According to NREL, reputable panels degrade as little as 0.1% per year, which means they will still be above 90% of rated output after 100 years. The trashiest panels NREL has tested degrade at 1.1% per year which would put them at 75% rated capacity in 25 years.

https://www.nrel.gov/pv/lifetime.html

This is very exciting. Does this mean the biggest continuing expense would be batteries if you wanted to self-sustain with solar?