Usually at that point someone puts in a new hybrid battery and sells it to someone else starting out driving Ubers.
What kills the hybrids is that the kind of people who buy these sorts of "peak appliance" cars tend to be the same kind of people who'll obliviously let some critical fluid run too low. You get orders of magnitude less of that sort of behavior in taxi fleets.
All this assumes proper maintenance, especially oil changes.
That said, the synergy drive is by design a very robust mechanical system. It has no dog gears, clutch or torque converter. I'm sure this contributes a lot to their long life.