If it isn't a competitor then it's not nearly as risky. You still need to be very careful though. Don't take anything with you. Don't use their laptop, servers, accounts, services, code, secrets, ideas, paper, clothing, anything. Walk away completely clean.
You could give them your shares back, but don't do it for free. If you want to be nice then sell them back cheaply or trade them for something you want.
You could give them your shares back, but don't do it for free. If you want to be nice then sell them back cheaply or trade them for something you want.