Luca,
Thanks for checking with us.
If the license is still valid, another developer can re-use the license. The key point is that each license may only be used by one developer. The same license can’t be used on multiple machines at the same time, though we do allow for multiple activations (for example, if the developer has a laptop used at home). However, there is a limit on the number of times a single license can be activated but you’d receive a message, in this case, and you can contact us to help sort that out.
I hope this clarifies the situation though there is more complete information in section 7 of this document. Please let us know if you have further questions.