I did that the other day - went to the car, got in, and it wouldn't leave Park. Played around trying to figure it out before realizing I left the fob in the house. I must have left the car unlocked in the garage (which is unusual, but I had been playing around with it that morning).
Another day I tried using the 2-minute Unlock&Drive button in the app (without carrying the fob) to go get the mail from our community mailbox. When I pull up there I leave the car on, put it in Park, leave the door open to grab the mail, and get back in. I got back in and it wouldn't go into gear! Aargh. Started to panic since I was blocking the mailbox. Thought I was gonna have to leave the car there and run home to get the fob. But then I tried the Unlock&Drive button again and it worked. Apparently if you use that, you have to reuse it again any time you take the car out of Drive.