No, it doesn’t actually need it, but it would be better, if it had one. Times are shifting, and more and more people want a basic income. Universal basic income is even an economically sound idea (though still too few people are aware of that). If people see a way towards a universal basic income that doesn’t involve governments and taxation, they might actually want to have that.
On the other hand, the reputation currency market is free. There will be a large variety of flux currencies. Some with basic incomes, some without. Some would even have completely different kinds of incomes (see my flux currency post).
The worst case scenario is a world that is much more unequal than the current one. Almost complete automation. People can’t get jobs, money, or even reputation, because machines can do everything better. Machines get all the jobs, money, and reputation. People stop caring about humans, because dealing with machines is so much better. Almost no human will get an amount of reputation that suffices for staying alive. Most humans are treated as criminal rubbish and get killed on the spot. The few humans who are on top upgrade themselves into immortal AI. The end… Of humanity.
Note that you have asked me for the worst case scenario, not a realistic dystopian scenario.
Would you like being surrounded by people who don’t care whether you die, because they see you as lazy and worthless?
Ah, right, just as altruistic people today save all people in Africa from starving… not.