When to pull financial plug on son? Doesn't care about his T50 college, he's just sort of...there.

Seems like a more reasonable target is “stay on track to graduate in eight semesters, and do not get academic probation or dismissal”. Typically this means 2.0 or higher GPA, no F grades, and no D grades for courses that require at least C grades (typically in-major courses).

Note that some students improve over the years. A famous example is Martin Luther King Jr., who earned a 2.2 GPA in his first year of college, followed by 2.5, 2.7, 2.67 GPAs in later years, graduating in eight semesters with a 2.5 GPA overall. https://kinginstitute.stanford.edu/sites/mlk/files/morehouse_years.pdf