To start with, we advise you to check the estimated date of delivery that is indicated on the project page. You may also check if the project creator has posted something in the "News" section, or has sent you an update to inform you of a possible delay in the delivery.
It may happen that project creators go through some difficulties when making their projects come to life. When it happens, we advise them to stay in touch with their contributors and let them know as much as possible of the evolution of the project.
Don't hesitate to send a private message to the project creator, or to post a public comment on the project page to notify them about the situation.