Current drop.io links work just fine. They just took away the ability to create new ones with a free account.
The reason he's encountering dead links is because drop.io drops are specifically designed to expire. You pick an expiration date when you create a drop. It's a feature. The service was not meant for long-term storage or distribution. Using it this way was a mistake.
Lesson: If you don't own the domain, you don't own the stability of those domain's URLs.