Question: Disappearing questions

Earlier today (30/12/2018), I answered a fairly routine question  relating to solving the PDE for a vibrating string problem where the initial string profile was given by a piecewise function. No big deal - a fairly simple answer. Only thing that struck me at the time as odd/unusual, was that 2-3 days ago there was a very (very!) similar problem which I had also answered.

These two problems were posted from different usernames, but I did reference the earlier problem in my solution to the later one, just because they were so similar.

Both of these questions (and obviously my answers) have now "disappeared" -how/why?

1. I can (just about?) understand that an OP might be allowed to delete his/her question, but I am surprised that (s)he can delete a complete thread - ie after response(s) have been provided
2. I suspect that both questions came from the same individual employing different user names (why?). I guess this is pretty much impossible for MapleSoft to verify, particularly if the OP has multiple email addresses??
3. Would I be correct in assuming that this is a method for students to get their homework" done whilst leaving little/no trace for their academic supervisors to find?
4. Since all trace of both questions have disappeared and I can't actually remember the usernames (or emails with which they are associated), presumably the OP could repeat this behaviour indefinitely?