For those who come across this issue, to re-add the user to the subscription requires some sql scripts and playing with Database Tables.

For emergencies only.

1. Manually re-add the deleted user via DNN 
2. in Database table, Edit DBO.Users.
3. Find the re-added user, then edit the Username & Email address (you just need to change these values, i put.old on all fields.
4. run this SQL - update the VALUES field, match the UserID with the old user ID or the end numbers on the reoccuring payment Invoice ID.
SET IDENTITY_INSERT dbo.Users ON 
INSERT INTO dbo.Users (UserID, Username, FirstName, LastName, IsSuperUser, AffiliateId, Email, DisplayName, UpdatePassword, LastIPAddress, IsDeleted, CreatedByUserID, CreatedOnDate, LastModifiedByUserID, LastModifiedOnDate, PasswordResetToken, PasswordResetExpiration)
VALUES (UserID, 'Username', 'FirstName', 'Lastname', 0, 0, 'EmailAddress', 'Full name', 0, NULL, 0, 1, NULL, 1, NULL, NULL, NULL);Go

SET IDENTITY_INSERT dbo.Users OFF
GO

This will readd the user to DBO.Users.

5. Edit DBO.UserPortals table.
6. Add in a new row with the same UserID & PortalID as the portal your website is on.
7. in your DNN website, you should be able to see the user in the list. Now add the subscription role and must have an expiry date to the user so the subscription module can renew it.

This will allow the user to reset their password & login.