Question 1: What IP Address recepient will see?
Scenario 1: You are connected to VPN and using a native email client such as Outlook: Then the header will contain the VPN IP Address
Scenario 2: You are connected to VPN and using a webmail service such as Gmail: Your real IP address or VPN IP address will not be part of the headers. Headers will only contain your webmail servers IP address.
Question 2: Will the real IP address be exposed when recipient replies?
Recipient will reply to your email address not your IP address. Let me elaborate. Emails are stateless, every reply or forward will be just considered like a normal email by your mail server. When the recipient will respond to you, recipient's email server will fetch the MX record from your DNS records. The recipient's email server will then send this email to your email server. Now, for you to access this email, you will have to sync your native email client with your server or access this email through webmail. This is what I meant by "Recipient will reply to your email address not your IP address".
Hope this answers your questions.