There are penalties for not submitting a deliverable on time or for not submitting at all:
If the project in question is a Speedy or a Contest, the first penalty will be that the Pro's stats will be affected. If a Pro has bad stats, they will not receive as many invitations to projects.
If the time to submit a deliverable expires we will reach out to the Pro and ask why they haven't submitted yet.
If they are unresponsive, we will consider that Pro unreliable and it is possible that they will not receive further project invitations.
Sometimes technical problems or personal situations beyond Pro's control do happen, so please let us know as soon as possible so we can handle the situation properly.
For more information see key traits to become a Pro.