You can leave your gateway untouched at the moment.
As far as i know you can not migrate the TTIG by yourself to TTSv3.
You can already migrate your application and sensors to TTSv3.
The Traffic will be forwared through your v2 gateway to the v3 Stack.
Be aware that other users reported some issues with RX windows and a workaround:
As long as you have a console access to the LDS01 you can have an eye on this issue.
I am unsure if it is necessary and safe to delete your application and sensor from v2 Console.
But i am sure:
Do not delete your Gateway from v2 Console!