At what point do you consider a pre-approval to have lapsed if no loan is created? When closing the application, what would be the best cllassfication for it? It's not a denial, would it be considered withdrawn by the lender? Any suggestion?

Anyplace specific I should be looking?

We give pre-approvals for 90 days. Towards the end of the 90-day period we contact the applicant to see if there has been any progress made in their hunt for a house. Depending on the conversation (or lack of response) we cancel the application according to normal procedures.

We went around and around on this. For a while, we withdrew loans that were approved but never converted. However, we were criticized by the OTS since a loan cant be considered withdrawn unless the customer expressly requests it (usually in writing). We ended up creating an "Approved not Accepted" field.
As for a time frame, we go with 90 days. After that time, the documentation is usually outdated anyway.

You should have an expiration date in your commitment letters otherwise they could be deemed to be good indefinitely. As such, you might want to have legal counsel review your commitment letters.