front shocks independent from rear shocks?

[ammophobia]

So I had a problem with my rear shocks, car still under warranty, so I came to the dealership and they replaced the rear shocks for free. My car is 3 years old. My question is, is it ok to have fresh rear shocks with 3 years old heavily used front shocks? Will it affect comfort and handling in any way? Should I replace the front shocks also?

Also, I heard it's recommended to realign the wheels after replacing shocks, when I told the dealership this, they said it is necessary to realign if the front shocks are replaced, but not with the rear shocks. Is it true?

Thank you very much :)