so yes, they should easily be able to retrieve the addresses associated with your proton wallet using the email you registered from.
But, consequently, does losing my seed phrase make me lose my funds forever?
If not, then there is no reason to give us seed words.
Don't get me wrong, I prefer having full control of my keys.
The way I see it, my optimal setup would be that Proton knows my addresses linked to my email so people can pay me directly via email, but they are agnostic to my private keys, so if I lose my seed phrase, I can't recover my wallet.