It's not a dumb question, but there isn't any single answer. It depends on what protections you have on your iCloud account. For most users, if you've lost your phone, but remember your iCloud password and have a new phone with the same number, you can get in. It's made even easier if you have another device already signed in, such as a laptop.

Luckily I do have a macbook, and try to put all my passwords in a "neutral" password manager, but this post has made me think about the edge cases of this sort of thing.

Ive always said, the number one reason I will stick with an iphone - despite any present for future dumb ux changes - is that I will always be able to physically go to an apple store and get someone to help me.