The process deregisters the phone number from the account; it does not shut down the entire iCloud account or disable iMessage entirely.
"iMessages" sent to your phone number will be translated to SMS.
iMessages sent to your email address will still be delivered to the account associated with that email address. They can be accessed on pretty much any modern apple device associated with that account.
It's rare that people intentionally iMessage an email address, but the interface is opaque enough that it's essentially impossible on an existing text chain to tell that you did (unless you're specifically looking for that information).
The behavior as implemented makes sense provided that every user made an intentional and informed choice when choosing to message a friend via phone number or email. That is, of course, not the case (and is not helped by Siri sometimes silently deciding to use a contact's email over their phone number).
"iMessages" sent to your phone number will be translated to SMS.
iMessages sent to your email address will still be delivered to the account associated with that email address. They can be accessed on pretty much any modern apple device associated with that account.
It's rare that people intentionally iMessage an email address, but the interface is opaque enough that it's essentially impossible on an existing text chain to tell that you did (unless you're specifically looking for that information).
The behavior as implemented makes sense provided that every user made an intentional and informed choice when choosing to message a friend via phone number or email. That is, of course, not the case (and is not helped by Siri sometimes silently deciding to use a contact's email over their phone number).