What does Mildred say that she will miss the most about living with Montag? What are Montag's feelings about Mildred leaving?

Mildred bemoans the loss of the "family".

She shoved the valise in the waiting beetle, climbed in, and sat mumbling, "Poor family, poor family, oh everything gone, everything, everything gone now ...."

Montag's feelings aren't really revealed..... though he seems to be shaken to the core by her leaving.

"A great earthquake had come with fire and levelled the house and Mildred was under there somewhere and his entire life under there and he could not move."