We can rotate keys, but if you discard them, you won't see the messages address to that key anymore. In all cases, you will need a collection of all your past receiving keys to move to a new phone, for instance.
Discussion
Wouldn't it make more sense to just link your nostr ID to your simplex ID for DMs and then when you want to DM someone you can choose whether to do it over nostr (if they're not a SimpleX user) or over SimpleX if they are.🤷🏼♂️
Simplex doesn't want to have a link to a known identity like Nostr would have.