Will a copyrighted code get into public domain once its copyright expires?

Question

Since source code license is protected through the Copyright Law (Berne Convention to be precise), and all copyrighted material will be in public domain for certain number of years, depending on which country.

1. Will a copyrighted source code, closed or open source, be in public domain once its copyright expires?

2. For closed source, can I ask the company for the closed source code once it got expired (just assuming based on what I've understood so far :-) )?

3. Assuming question 1 is true, how can I prevent a source code from getting into public domain once the copyright expires, if it's possible?