0x (ZRX) price, performance and general information

Hi, I'm interested in 0x and just looked codes, and I have some questions.
As I saw codes of 0x, it processes orders by

1 register order hash
2 register order hash that matches to1
3 atomic transaction happens

So, my questions are

-what happens if maker of 1 no longer owns the assets registered on the order when atomic match happens?
- are there any ways to check in advance if the above situation happened?
- is that order still available if the above situation happened?

Thanks

I logged into my account to try to remove some of my stake but it won't let me. The remove link defaults to the 0x documentation page: https://0x.org/