I've been using a pay as you go plan (not the always free) for years and I've never had anything deleted. As it's still got all the always free stuff I've also never payed a cent. I believe it just removes the barrier to paying, but you can add quota limits just in case.
I have 3 instances running (offsite motioneye [arm], wordpress [arm], wstunnel [x86]), but I have daily backups to my home server and plans in place if they get deleted.