Juan succinctly addresses point 2
Below the line is the original answer, which used to be how things behave. Now, it appears that proper comment replies are not retained in your envelope post-deletion. So when a post is deleted, your envelope no longer reports any comment activity.
However, there is an excerpt in the global inbox, which will give the user a link to the post. But, as mentioned by Juan, they can only see deleted answers so it will be useful only for answers.
For comments, if it is just a plain comment on their content, then no, they do not get any alert or message. I just checked back on an old deleted answer of mine, and checked my envelope's report, it completely skips all of the comments that were addressed to me on that answer.
However, if it is a comment reply with @name, then it overrides this problem and will be retained (though be decidedly awkward in some cases as you will only have the ones that actually mention your name). It will even work if it was someone else's content that was deleted.
Here is what this post looks like, with color coding the comments.
And this is what my report looks like, note the absence of comments in the timespan.