Hi guys,
thank you all for your replies. To update you, yesterday I was taking a better look at the whole thing, and I think there is no way around me not going to the mechanic to fix it.
So my understanding from what I see is that the bottom more plasticky piece has some sort of rectangular shaped pieces that are supposed to "click" with a more hardened plastic bumps. What I am seeing is that when the whole thing came apart when I went over the bump at the bottom of the hill, is that all those areas where is it supposed to "click" are gone.
Most likely, by it being violently removed, they were destroyed... which is really unfortunate. Basically, half of the lower rear bumper is unhinged from the top part, but it cannot click because those "bumps" are half gone.
Honestly, I don't know if this is a good design or not. Perhaps if the bumps that it clicks too were harder, I could've just put it back. Or perhaps the whole rear bumper would have been completely destroyed.
All in all, it looks like I need a full replacement of the rear bumper. I am not sure how much that is going to go for, but hopefully it is under 1.5k...
Again, thanks everyone!