That would be confusing, though, wouldn't it?
"Where'd the Personal Message icon go?".
Perhaps better to show an icon with a circle/slash through it and an alt text of"User XX has blocked your personal Message".
Same sort of thing when viewing a profile -- "Send personal message" could not be allowed to disappear, but would be greyed out and have the comment "User has blocked your personal message" appended.
There would be some additional overhead associated with that, as this is currently not checked on every single Display.php and every single profile.php
Then, in the suggestions (for To and BCC alike), you'd need a way to "gray out" names that have blocked you, rather than making them disappear completely.
If you make things disappear completely, you will confuse the users.