Completely rewritten is a bit of an overstatement. It depends on what road they choose. They could go with a react-API compatible library and the work should be

Completely rewritten is a bit of an overstatement. It depends on what road they choose. They could go with a react-API compatible library and the work should be minor. They could go to angular/vue/... which is more work, but they all work component based, so you can keep the entire structure.