peopleinside maybe just slightly. If a user doesn't have many discussions, you can go to the list and select Delete, then Delete permanently for each one. With this extension you could speed it up a bit by doing the same in a batch. But you will still need to manually load all pages of the user discussion list.
I'm not planning to add the control for posts at the moment because it's even more complicated than the others. And you probably want posts as well.
To limit damage I will probably also not allow direct access to Permanently delete in this extension, I will require to first soft-delete, otherwise it's too risky, because with very few (mis)clicks you could destroy every single recent discussion forever.
It's probably not very complicated to make an extension to one-click delete everything. The problem is just what might break if content is deleted permanently, and how to control what gets deleted in case you don't want to delete everything. In general I'm pretty reluctant to implement anything related to perma-deletion because if not done properly users (in this case, admins!) might accidentally delete stuff forever and then find they don't have a backup...
Is it really a common use case to have to delete everything from a user's history? In my experience users that get suspended and content deleted are spammers, and they generally don't have the time to post a lot of spam before being deleted. So it's not very difficult to delete their content manually if an extension like Stop Forum Spam didn't do it already.
