John,

If it is a small repair, you may want to test out a product at Lowes.  Homax ceiling texture.  I'd suggest trying it on a scrap piece of drywall (make sure it's at ceiling height for testing).  Jayme and Phillip both had great ideas.  Perhaps yet another would be to just remove the popcorn all together.

Samantha,

Typicaly most repairs are noticable and replacement it best.  If you simply need to cove the hole and this is a typical way you keep puppy indoors, you may consider purchasing a piece of metal to cover the hole and prevent more damage.  Home Depot #800537 is a quick idea.   

The caulking mentioned is fine to seals the gape but you may need somethingto back it other thatn backer rod. in that case you may need a small amount of Rockwool insulation to pack into the void befor applying the caulk. This is a link to the product https://www.rockwool.com/applications/exterior-walls/firestopping/

If you only need a small amount check with a local insulation company to see if they will sell or even give you the smaill quanity you need.

I agree with Jared. You will need a high temp sealant.

Good Morning,

Nice space.  Its hard to tell from the photos just how big the space needing to be filled is however 

Dap 18854 High Heat Mortar Raw Building Material, Black

should work well. It can likey be found at you local hardware store of online

https://www.amazon.com/18854-Mortar-Building-Material-Black/dp/B0006MXS4C/ref=asc_df_B0006MXS4C/?tag=hyprod-20&linkCode=df0&hvadid=167127061369&hvpos=1o5&hvnetw=g&hvrand=16226564078373131268&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9032160&hvtargid=pla-307130896304&psc=1

Best of luck and Happy Holidays

Jared

Per ANSI/IICRC S500 Standards and Reference Guide.

"Restorers should consider drywall restoation when it can e verified that no structural integrity has been lost.  Dywall can be restoragle if the water is Category 1 or 2, there is no obvious swelling, seams are intact, and there is no idication of fungal growth.  Drywall should be replaced when contaminated with Category 3 water, damage is obvious (e.g., swelling, seam sagging, seperation), fungal growth is present on paper coverings on either side, or when blown-in insulation materials behind the drywall have likely packed down."

The drywall that has water damage should be removed. The wood studs might also need to be replaced depending on if there is mold or rot. The insulation behind the drywall should also be replaced. The base molding might also need replacing as well as the flooring.  

Blow in, but will have to hide it with a new ceiling I believe...

Blow Insulation 

Energy efficent windows are a good investment.