Ajax with PHP - Is Ajax a replacement of server side "View" of MVC?

Ajax with PHP - Is Ajax a replacement of server side "View" of MVC?

I am using PHP mvc framework (Codeigniter) for my web blog.
I am going to implement Ajax for the first time to see the real benefit
myself.
I guess what I've done from the view such as formatting and display result
on html page can now be replaced by the Ajax implementation. So I guess
the view of the the server side mvc would no longer be used.
With a form validation, it is suggested to have both client and server in
case javascript gets bypassed. I guess the same concept applies here with
Ajax when javascript is disabled from client browser. I mean, you get no
data when it's disabled. What would be the back up solution for this
scenario like how validation can have double layers?