Certified GKH Gardening Expert
Your photo did not come through, unfortunately. If the entire top was lost to the graft point, your tree will likely never recover. It will likely result in the rootstock taking back over.
If it has only broken a portion of the top and there are still weeping branches, then it is possible for it to recover.
Here is an article that will help you to care for the tree: https://www.gardeningknowhow.com/ornamental/trees/weeping-cherry/snow-fountain-cherry-info.htm