This will kill almost all new investments immediately. Investors will balk at ~50% of the shares of a brand new company being owned by an ex-founder no longer involved.
How does it matter if it’s going to be diluted anyway? Investors will get their post-money 30% equity, or whatever it is, and rest of the shareholders will keep their proportion of the 70% (and ~50% pre-money gets diluted to ~35% post-money).
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.
From an investors point it's very unattractive to invest in a early-stage startup where half of the shares are in the hands of a person not working there anymore.
He'd need to raise capital at some point, new investors could buy your shares at a higher value.