It will never be “end of life”. There are retro consoles that people are buying just for running SNES or GameBoy Advance games. Even those are perfectly functional for their purpose. Even if the Steam Deck got hard locked to only run games released up till 2025, it will still have enduring value. EoL can mean the battery is too degraded, but the battery is replaceable.

A “soft EoL” will realistically come when much much faster hardware is cheaper, the Steam Deck is out of production and it starts struggling to play even indie games. At this point, buying a secondhand Deck for £100 is still going to be a bargain and get recommended for emulators, retro gamers and patient gamers.