Answer: In my experience the odds of this working are very slim indeed and nil if the pieces are completely severed and/or have dried out but you could try to graft it back on. Align the pieces as though mending broken china, as close as possible to the original placement taking extra care to align the bark layer as well. Tape firmly with electrical tape. (Grafting wax seal would be better but it is not usually readily available.) Then you will have to splint it to try to support the weight of the tree. I'm really sorry about your tree.
Although it is a bit late for this point, unless the tree is in a very windy location it is not usually necessary to stake a new tree. More recent studies have shown that the vibration occurring on an unstaked tree actually stimulates roots. In any case, the guy ropes should never be so tight that they could snap a trunk.
You might want to check with larger nurseries in your area and see if they could order a replacement for you.
Q&A Library Searching Tips