The one thing I wish rehab would have better prepared me for was what to do when others relapse.
I can recall several occasions not too long after I and several peers (to whom I had grown pretty close) were released where someone relapsed and none of us knew what to do. We were at a total loss sometimes.
I had a conversion with a counselor there after some of these instances and asked why we weren't better prepared for this. He explained (in a nutshell) that we need to be most concerned with keeping ourselves sober and not so much everyone else. I got the impression too that this kind of thing (friends relapsing) all too often and the prospect of that happening isn't exactly a desirable topic for those who need to be focused on themselves for a while.
While I do think that it's good that you're thinking of your peers and how you can help, I learned that in early recovery my focus needed to be on me.
Had I been in that situation, I would have said something - that being the case now as I've been in recovery for at least a little while. Though had it been back when I was earlier in my recovery, I would have said nothing. I wouldn't have known what to say. And I don't mean that there is any right or wrong way - just me and what I might do.
I also suspect that the therapist was well aware and perhaps did not say anything because they wanted to see how you would react to the situation - just a guess...