I’m a bit confused. If a subscriber is tagged when they enter via a form, they should all be tagged. I don’t think anyone is ‘forced’ to leave an automation just like that or randomly unless you have an opt out or trigger set up, which then it would be by choice and not by force.
I think you can put an exit at the end so when people are done with the automation they’re all ‘out’ of the automation. But ultimately, it’s a visual and linear process so you’re in control of what happens and what you’ve put down is what will happen, there isn’t anything hidden.