If a user is mentioned in the newsletter as a question asker or answerer, a tiny icon for their gravatar appears.
However, if the user has been deleted, that does not work.
Example from a recent Skeptics.SE newsletter:
Looking at the HTML, the source link is empty:
<table> <tr> <td style="padding-top: 0;"> <img src="" align="right" width="18" height="18" /> </td> <td style="padding-top: 0; color: #AAA; font-size: 11px;"> answered by <a href="http://skeptics.stackexchange.com/users//user288?newsletter=1&nlcode=58385%7c8169" target="_blank" style="color: #000;">user288</a> 35 votes </td> </tr>
As you can clearly see, this is a critical bug; the whole SEI team should immediately drop everything to work on this immediately before more people suffer. Another entry for the Lowest Priority Bug of the Week Competition.