Aww, last days make me so sad. Boo!
I'm going to tell you, though, I've gotten a lot better with my good-byes. On my first trip (at 29 years old), I sat at Downtown Disney on our last day and cried my little eyes out.

No, really. At the tables by the water right near Ghiradelli.
After we moved to Georgia and started going yearly, I got a little better, but I always had to visit a park on our last day...even if that meant getting home really late and having to work the next day.
Now, we've moved it up to going a couple times a year and I can leave directly from the resort in the morning on the last day. I still have to visit the gift shop one more time...and maybe take a look at a few more things around the resort before we leave....and maybe, just maybe, my husband has to practically drag me to the car....
But it's definitely better.