Looks to me that the two strings are too tight and are likely the cause of the death of the tree above that point. It also looks like the new growth is just above the graft line, so at least you can possibly regrow a new tree with quality fruit. Like CJ said, cut the strings and keep an eye out for suckers from below the graft line. By removing the suckers you can use that energy for growing a new top faster. One other possibility is to let it grow however it wants and then you'll have extra grafting sites for adding scion wood should you need to replace the top. Best wishes.
If the tree needs support, try making a small cage around it instead of tying strings to it.