Yeah, I think it will be better if OP can reach an agreement somewhere in the middle where they retain just enough shares not to interfere with future investmen

Yeah, I think it will be better if OP can reach an agreement somewhere in the middle where they retain just enough shares not to interfere with future investment. 5-10% of something is better than 49% of nothing. Plus they can collect some cash while the other founder and/or company still has money left, which again is strictly better than shares of an uninvestable company.