Is the storage plan stay after upgrade

You will lose the ability to put any more data into the storage. If you have not put any in yet, then that means it is taken back.

If you already have data in the storage before you cancel it, Apple state to backup your data - if you reduce your data plan - , so you don't risk losing it. I think that means they will delete the data at some point. See:

https://support.apple.com/en-gb/HT207594

misharjl wrote:

After upgrade the storage plan (eg : upgrade to 50gb) then cancel the renewal, is the 50gb will stay or will be take back?

Read here for details => Downgrade or cancel your iCloud storage plan - Apple Support