Apart from the possible physical consequences I think it's very ill-advised to roll while on a zyprexa course. As you undoubtedly know zyprexa is prescribed for very serious afflictions, sometimes caused by chemical imbalances. If you then add a substance that further disrupts this chemical balance - like MDMA - you are in my opinion running the risk of worsening the affliction. This is not something I say just to cover all bases, I believe there is a real possibility for this to happen. This really is a very bad idea I think. He should first take care of his psychological issues and be medication-free for a while before he tries to roll again
As for the side-effects. Zyprexa is partly a serotonin antagonist - for 5-HT2B - and partly serotonin inverse agonist - for 5-HT2A, 5-HT2B and 5-HT2C -. There is a difference between the two but when talking about MDMA they essentially mean the same, they will partly or completely block the serotonergic effects of MDMA, leaving you with just some dopamine and norepinephrine activity. This I think produced the side effects. I think they were the same side-effects as with any other MDMA roll, but because all the serotonergic activity - which indirectly produces the love and empathy MDMA is known for - was absent they stood out much more. Serotonin syndrome is I think impossible from this combination because of the tempering effect zyprexa has on serotonin release, I think it isn't possible that enough is released while on zyprexa to produce serotonin syndrome
What side-effects exactly are you talking about if I may ask? And how severe were they? In any case yeah he will be OK, but obviously he shouldn't roll again until medication-free