Does it ever happen that a completely severed acl heal?

ACL Reconstruction: Yes, you can still have an acl reconstruction. Acl tears do not heal on their own & having it replaced can help you maintain a healthy/ active lifestyle in the years to come. The acl is a major knee stabalizer, and can provide security to your knee that may prevent further damage to nearby tendons, ligaments, muscles, articular cartilage, meniscus, & bones when compared to a "loose knee"

No: Unfortunately, acl's are intra-articular and when they tear cannot heal. People will recover from the injury and feel almost completely normal a few weeks after tearing the acl but have a false sense of security. Many think that the problem is gone or the acl has healed, but it has not. The sense of instability will roe-occur with lateral or twisting activities. Surgery is very successful.