How long should scab remain in place after a wisdom tooth removal?

It varies. The "scab" is actually the blood clot matrix which is allowing for bone to grow in the socket. The gum tissue will also eventually close the hole. Just keep the area clean and avoid trying to pick the area. If any problems see your dentist.
A few weeks. The scab can remain a few weeks after the extraction. It may look white because it is wet. Use warm water rinses and vitamin c to help healing.
5-21 days. The scab or clot that forms after an extraction usually appears as a whitish substance in the socket. Depending on how difficult the extraction was, how healthy you are, and how well you follow post operative instructions, it may take several weeks before it is completely gone. See your dentist or surgeon if you think something is wrong.

Related Questions

Will wisdom tooth removal cause a scab?

Not really. Because your mouth is a wet place, scabs do not form like on your skin. Instead a blood clot forms in the area where the tooth was and over time tissue fills in from underneath to heal the extraction site. If you have sutures put in to close up the extraction site, you may never even see this blood clot at all. Read more...
No. Not a true scab, but a blood clot will form. Best advice is to make sure you evaluation and treatment is by the wisdom tooth expert - oral surgeon. Read more...