I’d be surprised if the UK just lets him rot in the Ecuadorian embassy. Ecuador is choosing to interfere in the British justice system and providing encouragement for every 2-bit thug in London to pay off the ambassador of a third-world country for a get-out-of-jail-free card. They could press for them to be forced to hand him over on the grounds of violating their charter as an embassy, or in an extreme case, outright shut down the embassy (Ecuador would retaliate by doing the same, but then so what? They’ve already made it clear that they don’t care for their international relations with the UK)

Honestly, though, I don’t think Assange would be willing to sit in the embassy for years on end even if the British permitted that. It doesn’t fit his personality. Wouldn’t be shocked to see him make a break for it after a couple months of failed attempts to find a safer way out of the country.