I personally know two people who were attrited. Yet both of them, after doing poorly for more than four weeks, actually just DOR'd. They were both on "battalion probation" and ended up getting boarded several times. Yet in the end, the board just ended up asking "do you really want to be here?" And they finally made up their minds then and there to just be done with it.
So I assume that barring a blatant integrity violation, they'll keep you there as long as you can continue to convince them that you want to be there. Heck, I know of a guy that got through after kicking off the season with three pullups on the inventory PFT. He graduated with only nine, but he graduated.
Btw, those other two were enlisted Marines, so nobody's exempt from possible failure.