If this was my son, I would wait until next fall. You stated your son is concerned he won't be able to cram it all in, and his concern alone would be enough for me to suggest he waits. And if your son is not a strong student, pushing through might be too much for him. You wouldn't want to set him up for failure, but ultimately this is his decision.
As other people stated, cramming 5 weeks of education into what little of the semester is left ----- it is a great disservice to the students. From a cost standpoint, you are being ripped off. You paid for those 5 weeks of instruction, and your son did not get those 5 weeks of instruction, yet he's forced to learn all of it in a compressed timeframe, in addition to the current material. It's plain as plain that he's being shortchanged, as are all the other students. Not a good value, I would want a full refund. I would feel cheated, almost defrauded even. Those professors are supposed to teach and instruct those students and for those 5 weeks they didn't.
I know college courses are fast-paced, but those students deserve to be properly educated and taught thoroughly --- not rushed --- with enough time to process, absorb, and retain all the material. Fast learners will be able to cram 5 weeks worth of material in their heads and independently educate themselves, but not everyone is like this. If everyone was like this, we wouldn't have much need for professors or tutors.
But if your son does decide to push through the semester, I hope he gets all the support and tutoring that he will need. You wouldn't want him to just squeak by.