When Toys “R” Us sought bankruptcy protection last September, there was good reason to believe the iconic retailer would work through its problems and emerge a leaner but viable company. Its suppliers were confident enough they continued to fill its shelves with toys.

On March 15, however, to the surprise of most people involved, the 70-year-old company announced it was shutting for good. Some 33,000 workers lost their jobs. Vendors now face at least $350 million of losses. The toy maker Mattel Inc. took a big hit to its bottom...