A person can be impeached regardless of whether they currently hold office or not. In addition to removal from office as a result of impeachment, it is also possible to permanently bar that individual from ever holding any office.
Not that any Dem would vote to actually remove an impeached Dem. However, impeachment proceedings could be started, get the press coverage, and then during the house proceedings, halt the impeachment and further the action to a special prosecutor for criminal charges. In the case of Hillary, this would be the better option as it will drain her finances and tie her up with legal proceedings. Essentially limiting her campaigning and fund raising.
I think you’re dreaming.
May be pleasant dreams but dreams nonetheless.