So, in which order do they retire?

Out of these vet's, which order do you see them retiring in?

Cro Cop
Big Nog

am I forgetting anyone?

This is how I got it:

Hughes(after next fight)
Wand (after 1 more)
Cro Cop (after 1 more)
Big Nog

I think your list is spot on.

Hendo is the oldest, but I think he has more left in him than the others. Phone Post

I think Anderson And fedor are going soon also Phone Post

 Ace has plenty left and IMO he beat Hendo. He's very relevant and will beat Nog. 

Cro Cop-Pudzian would be a big money maker. That fight is always there for him. I could see him taking some KSW fights.

Fedor and Wand will be the next to go

I think Wanderlei has fights left...he came off of a very long layoff.

If he gets knocked out again...then yes he needs to hang it up.

I'm sure it's hard for any fighter to call it quits after being in the business forever.