So the other day this happened, the car was tightly parker so while taking it out of the garage someone wasnt paying attention and broke the mirror.

My question is, would this require full assembly to be replaced or just the outer casing.

This mirror had problems tilting down during reverse and was planning to get that fixes under warranty but now I am sure they wont entertain that

 

From the graphic below it appears you can do either.
#7 & 13 designate left / right whole mirror assemblies $$$, OR #10 & 16 designates left / right mirror cover housing set $$.

You can always try to have them repair it under warranty though they (service dept) may give you grief and say tilt down function was disabled due to damage; however, you would have to weigh the cost of total assembly / color matched replacement versus the removal / disassembly / repair / reinstall cost to just replace the mirror cover set & repair the tilt function.
Mirror - 2019 Acura MDX 5 Door TECH (7P) KA 9AT (acurapartswarehouse.com)

 

Thanks this is helpful, though looks like the name of color is different between US and Canada, It shows Extreme Crimson Pearl while mine is Performance Red Pearl not sure if they are just different names for same color or different colors :|

 

Experiment with the 'Body & Trim' selection on the link provided, you may find the exact color.
I just picked '5 Door TECH (7P); KA 9AT' because I could not find the 'ELite' as part of the selection?

 

Thanks will do