It's generally understood that finding a talented Dev team is far harder than transitioning a team to a new technology. Many company's have transitioned code from platform A to platform B without building a new team from scratch.

Not because everyone will make the transition but because what separates a great QT/.net/java/c++ developer from an average one has vary little to do with experience. So, while such transitions are a great time to remove deadwood, and you want to find some experts in the new stack laying off the old team is expensive and rarely worth it.