What is the process for leaving a company (or even a group/division) in terms of code support?

Is it best to handle all questions? Do you give the remaining developers access to yourself as a future resource? If so, is there a way to not give full access?

I've experienced first hand where answers about the general software arthitecture from the initial developer would be invaluable.

I understand that if serious assistance is needed, than it becomes a typical case of employment negotiation as a support contract. However, should serious assistance be required, what steps can you make to ease that process of contacting you?

I was thinking of doing something like making a (YOUR_NAME)_codesupport @ (YOUR_FAVORITE_EMAIL_CLIENT).com address.

My Situation Specifics:

I'm a co-op student, and as such bounce around companies on 4-month stints. This means introducing myself to a lot of new code bases, as well as leaving a fair share of orphaned code behind when I leave a company. I feel bad if I leave junk code around.