I would burn the entire thing to the ground and piss on its smoldering ashes before I would allow someone to take advantage of 11 months of my work just because he thinks he can make more money for himself if he positions himself as a solo founder.
"I would spend $15,000 of my own money and 8 more months of my life during which I deed control of my adrenal system to this stupid controversy and get little else done, and ultimately reach at best the same outcome as I'd have achieved walking away amicably, less expenses, before I would allow someone to take advantage of 11 months of my work".
Greater good/game theory argument. If we're all spineless, we just make it easier to be taken advantage of. Burning it to the ground is akin to MAD, but it only works if it's a likely outcome.
I'm not sure what I'd do but I'd view a 51/49% split as suspect from the start.
Their main claims to success based on OP's description are that they show up in search engine results and are only $60K in the red. If that's success in 2020 then I can launch a dozen successful startups by January 1.
They said they have 60k users. If you can acquire 12 * 60,000 = 720,000 users for 720k in less than a week I think you'll have a lot of people beating down your door.
