2
Not that I am aware of.
We certainly does not have
if ($concurrentUserCount > 200) die;
Anywhere
200 concurrent users is quite a lot, though, and I would indeed throw the ball back to Surpass. I am not saying that XOOPS is fantastic for very high-traffic sites as I do not have the sufficient factual backup (I don't have anything saying the opposite, though) but if the page cannot be served due to too many users online, then it is a problem with the server's resources (which may be caused by XOOPS' inability to handle that number of users without drawing too much on the resources) and should be visible in server logs/stats for CPU, Memory or bandwidth usage.