Creating dependent models in the same form

Hey Guys,

I just wanted to get some feedback on what I have done here and how to
improve it. As I am just starting rails, I think this would be super
helpful if any of you have time

So I have a table of songs. Each song could have multiple people One
person could be involved in multiple songs.

I therefore have a M2M relationship (Song <=> People). My join table
is called Songwriters.

When a person wants to add a new person as a songwriter on a song,
they have the option of either selecting from a drop down of the
current songwriters or entering the information to create a new person
right there in the form.

Here is my controller method that the songwriters/new action goes to:

def create
    @songwriter = Songwriter.new(params[:songwriter])
    @person = Person.new(params[:person]) # => To hold the potential
new person data

    if new_person? # => A new person needs to be created
      if @person.save
        @songwriter.person_id = @person.id # => Replace the id of the
person with the new one
      end
    end

    respond_to do |format|
      if @songwriter.save
        flash[:notice] = 'Songwriter was successfully created.'
        format.html { redirect_to(song_songwriters_path(@song)) }
        format.xml { render :xml => @songwriter, :status
=> :created, :location => @songwriter }
      else
        format.html { render :action => "new" }
        format.xml { render :xml => @songwriter.errors, :status
=> :unprocessable_entity }
      end
    end
  end

  def new_person?
    params[:person][:first_name] || params[:person][:last_name] ||
params[:person][:person_alias]
  end

So the first question is, what happens if for some reason, the new
person does not save? How do I stop the action from continuing?

Any help that you guys could offer me would be most appreciated! I
just want to be in your shoes right now!!!!