I can't find see anything in the requirements supporting this. The closest I see is:
This document deliberately leaves some issues unspecified, and some problems unraised
The requirements say nothing about this issue specifically, but there is some justification for addressing unraised issues if we deem them important. But I'll agree with Max that you shouldn't feel you
need to worry about disconnected clients. And if you do handle them, make sure your solution works correctly, and is as simple as possible for what it
does do. A simple solution that doesn't handle disconnects is definitely preferable to a complex solution that doesn't really work. A complex solution that does work is risky too - make sure the function of each part is easy to understand.