Would they, though? That's the key question that I believe this study (and others like it) fail to address. Depending on the basic income amount, I believe it would be possible to live a fulfilling (if somewhat minimalist) life without needing to supplement that income.
Yes, this requires employer flexibility and the move from 40h->15h per week grants much less freedom than stopping work entirely but masses of people suddenly being content with a minimum amount of money does not sound convincing to me at all.
Living off the basics is pretty dull. Most people who live ascetic lifestyles by choice usually come from a position of relative wealth and choose it more as an aesthetic or affectation than anything.
With BI I could spend more, but I would still keep on working towards a relaxing financial freedom where money is not a problem at all.
Anecdotally my friend is part Native-American and gets 4k/mo from the tribe's casino money and they're bumping it up more soon. She's chosen to be a stay at home mom.
All in all, I think there are enough people that things would be fine.