Ethereum does not store your public key. It pulls the key back out of each signature you make and then drops it. The signature, though, is permanent, so the key is permanent too. Anyone can recover it from any transaction you have ever sent, today, or in forty years.

That is fine for as long as turning a public key back into a private one costs more than the universe has time for. It stops being fine the moment it doesn't, and an adversary does not need the machine today to use it later. They need a copy of the chain, and everyone has that.

Stealth addresses are in a worse position than ordinary ones. Their whole claim is that only the recipient can tell who a payment belongs to, and that claim rests on a secret both sides derived from two public points sitting in the open, forever. Break the curve once and every private payment ever announced unwraps at the same time, backwards, including the ones made years before the machine existed.

LETHE takes the curve off the path. What is left is keccak256: the hash Ethereum already runs on, and the one thing in the stack a quantum computer does not take apart.