G Suite Migration – Resolving Lost Alias Emails

When using a domain alias, every account in your domain gets the other address at the alias domain. You can't change or remove this for a single account.

To address your direct question, you can not remove john@alias.com from the account john@domain.com. If you have renamed the account to john.suspended@domain.com, rather than adding john.suspended@domain.com as another alias, then john@alias.com should either no longer be an alias on that account, or you should be able to remove it.

If you can't, I recommend contacting Google Support as it appears this is bugged.

You need to open the page for the email and select the three dots where you can view settings for the migration. You should see an option that says exit migration. Once you select that, then you will be prompted with the email, calendar and contacts option when you try to migrate your data again.