Sure they can have fun.
But I'm not sure they can have a nice day , be happy and decide "Well tonight I'm celebrating , gonna put my pants on my head , drink myself silly , run down the street naked and go find someone to play "ride the Bull"".
And with the kind of not really funny job he was doing back then (hunting rebels) , I assume in Seheron , he probably needed to blow a fuse .
And I'm not sure the Qun allows that .
No the Qunari certainly do not lose control like that. The equivalent of doing so for us, would be something like a "proud alcoholic". However the Qunari can after their days work is done, relax and have fun with the friends and collegues. They just maintain control, since the loss of control of one self is practically taboo for Qunari.
Just to be clear, I don't care if they get shitfaced. I'm a boring sober dude these days myself. 
The issue is more complicated than that. They don't seem to evaluate individual actions or mix n match behaviors, or just go with the flow, make momentary decisions. It's all about conforming to a fundamental idea of existence. Their "true nature". To simply "be". Veer from it and you fail.
Which still wouldn't be a problem to me either, but they wish to ascribe an "existence" for everything else too. They're not content just doing it on their own. They want everyone else to conform too. They are busybodies and meddlers. But oppressive ones. Worse than any finger wagging grandma.
ALL ideologies are meddlers and imposers. The Qunari even though they ascribe to an idea of control of one's self and surroundings, does not mean that they are incapable of humor or having fun. I only have to bring up Sten which had an extremely dry sense of humor (which is also why much of what he says should be taken with a grain of salt).
It's just that if they go to far they are excited or reeducated.
Yes if they lose control too badly (or too often, we don't really know the criteria here) they will have to be reeducated. Obviously when the Qunari values control of one's self as much as they do, they cannot tolerate someone who routinely disrupts public order.