Instead of deleting the member, wouldn't you just want to make their account inactive (not visible).
That way you don't have a bunch of posts that say author "n/a" on them.
You could add a visible field (0/1) to the MEMBERS table.
ANOTHER solution might be to move the information from the MEMBERS table to the MEMBERS_PENDING table (if you have email verification MOD in place).
The member would then have to reverify their account by clicking a link in their email. You could then delete them from the Members Pending link in Admin Home.