We have put together a short survey to capture your feedback in terms of what BT can do when you experience home Wi-Fi issues. We would appreciate it if you could take a couple of minutes to complete a short survey. Read more from here, Fix my home Wi-Fi
Doesn't matter what you have decided, the decision isn't yours. BT will at some point move your BTYahoo email to the BT mail system. You have no say in when that will occur.
I’ve decided that the status quo is satisfactory and not to change. There are more important things in life.
As has already been said, it is not your decision. You will not be able to remain on the BTYahoo system. The system is being closed down and if your account is not migrated, albeit that is not an option, it would result in all its folders and contents being irrevocably deleted.