You can just switch between the devices (Windows App/ Browserversion). The game always asks you if you want to use the local game data or the data from the server when you switch devices. I would guess nothing really happens when you delete the trail account. But then is the question why make one in the first place just for the white wale ? . The exception here would be if the data is saved at trail and not on a GI Server i cant answer that.I have a question if you connect your account then you cannot return to windows account or you can if delete the account in the trail ?
To the topic of the thread "the signin to save progress" for windows players is probably missleading because you cant access your old GI link with a fresh account so you cant restore it with just one device you need the second device to access it. Thats why you need to link your game (windows app) to a browserversion so you have a second device connected to the server game data for your game. If this is better then a localstate backup i cant answer only time will tell.
I hope that answers your question.