www.GMTNation.com is where you need to be for the Envoy/Trailblazer
Good ol' Galvanic Corrosion!
You are not screwed, but you have some work ahead of you...
Start by doing yourself a favor, Pull the caliper off, and put it to the side, undo the tie rod end from the knuckle, unplug the ABS wire and pull the wire out of the clips, and disconnect the lower ball joint from the lower control arm, do the same for the upper control arm, and take the 2 bolts out of the strut at the top. One last thing to do, and it can be done in 2 different ways. Take the 2 bolts off where the lower control arm meets the control arm mount, or, take the big nut off the lower strut mount and pound the boss off the tapered clevise. I prefer to take the lower strut nut off, as this will make it so you dont have to compress the suspension when putting it back together. This will allow the entire spindle assembly to drop out, Leaving just the upper control arm, and lower control arm depending on which way you did it.
You might already be at a point you can just undo the 2 upper strut bolts, since you do have the CV Axle out.
You will need this room for the next series of steps...
CAREFULLY drill holes in the remaining chunks of the disconnect to break it up. Once you get it to break a chunk out of that part the rest should pop free. Just don't drill too deep and go through the oil pan!
You are not the first, and certainly not the last, that has had this happen to them.
Dont know if you will be able to see these pics of others..

Hello to all the fellow GMT users on here. I am new to forums but think I have the gist of it. I have recently been having trouble with my 4x4 not engaging in my 2004 trailblazer. Switch it over to 4hi and the actuator and transfer case whirring sounds are present and the indicator light...
gmtnation.com
When putting it back together, use some anti-seize lube on that collar to prevent this moving forward.
There is a recommended disconnect, that has the lowest occurrence of failures, but I cant remember what the brand name is.. Been forever since I dug into that thing!
Edit: That axle end piece you see there.. It will slide right out, and allow you more room to fight with it.