IB let me try to give you a bigger picture. I teach college students for a living. Their grades even in the first year of college are typically a real mess. I have seen SO MANY students turn their lives around after that first year. This is why many times when people apply for grad school, whatever they score in freshman year isn't even "counted" as it's a "transitional" year. And this is assuming that they had a NORMAL h. s. senior year and first year of college.
We actually have a committee of faculty who reviews student GPAS in first year of college who lets the students come in and present their case, and let me tell you, students who have any family issues going on, like a divorce, are listened to.
I realize he isn't in college yet...and you know if he wants college great and if he doesn't, no problem. But what I'm saying is that college faculty and admissions are incredibly aware anymore that at least half of our students, if not more, come from really tough situations like what you and yours have been through, and we take all of that into account when it comes to admissions and scholarships, etc.
I would urge your son, if he intends to apply to college, to be VERY up front about the trauma in his life that occurred in his senior year. If he had terrific grades, and then they plummeted, THIS is the reason. What he had to deal with (and you) is the reason for the problem. Not a lack of ability or intellect, but real life and real problems.
These are things that counselors do look at. Tell him to be honest.
What colleges are looking for are students who can pull themselves together after a trauma. There are usually programs in place to help if they are behind, and there is nothing more "American" than picking yourself up if your life experiences a fall.
I can't speak to "all" colleges, but this is honestly the very type of student that my college tries to recruit. Students who have faced something difficult who have the courage to do better.
Your son facing this difficulty is not necessarily a bad thing.
M45 Bomb 6/09; EA 6/10; Divorced 1/11 Proud single mom of 7 little feline girls and one little feline boy "Fall down 53 times. Get up 54." -- Zen saying