What happens after an official is impeached?

I'm glad you just said "official" and not just the President. I found a pretty decent general "definition" at http://www.usconstitution.net/glossary.html#IMPEACH

"Impeachment - Impeachment, in the U.S. and Great Britain, proceeding by a legislature for the removal from office of a public official charged with misconduct in office. Impeachment comprises both the act of formulating the accusation and the resulting trial of the charges; it is frequently but erroneously taken to mean only the removal from office of an accused public official. An impeachment trial may result in either an acquittal or in a verdict of guilty. In the latter case the impeached official is removed from office; if the charges warrant such action, the official is also remanded to the proper authorities for trial before a court."

So there is something like an "indictment" and then a "trial" -- there are 2 parts to the process. For the President the US Constitution specifies the "crimes"; State constitutions don't always do this.

In situations where an official refuses to leave office after a finding of guilty, the State Legislature can force the removal. Neither State or Federal government can be disrupted by a wayward official, so extra measures could be taken, including locking the now-ex-official out of the physical office, prohibiting the ex-official's now ex-staff entry into the office or building, and technically, the parties could be arrested for trespassing. However, most ex-officials are too embarrassed and therefore comply with removing their possessions and themselves from the building and relinquish official duties.

Ohio recently had an Attorney General removed (2008 or 2009), and we're all aware of the impeachment of former president Clinton.

One further point, no official is above the law. If their misconduct involved illegal acts, they are subject to prosecution. They must also repay public monies if they used them inappropriately. Charges of tax evasion might be brought in some cases.