They left him and I believe went overseas for armour plating and such.
Or, perhaps they were armored somewhere else and then sent overseas . . .?
And yes, no more 2500 Burb. They stopped in 2010 iirc, and around 12/13 they started building the government only issue 2500 burbs(most get sold to foreign governments I believe).
GM does look like it is trying to make the new Burb's tow capable again but, for the price point, Ford and Nissan have arguably just as capable platforms for a very competitive price.