Removing access immediately is important for 2 reasons. The first is obviously security. Then 2nd is figuring out what he does & making sure somebody else has that access & knowledge.
Beat me to it. When I saw "finishing up projects," that immediately raised a red flag. All projects should immediately be turned over to other staff, and the short termer can watch over their shoulders and answer any questions. It may make sense to let them keep email and IM during the time, and maybe even read-only to code to help look up issues. But that's about it.
For me it's not about security of the company. It's security of the person leaving, so that they can't get blamed for breaking something during that time. But the most important thing is knowledge transfer. Two weeks is a very short time to document all the little things that were picked up during their tenure.
My biggest complaint recently has been people leaving without proper knowledge transfer. Even after I emailed managers on that point, and was told to try to stop scheduling meetings with him. "He's too busy." Sigh. Now I'm left picking up the mess he left behind.