He got "yeet" by Dabi. And i dont think he is dead, maybe he got major damage after that attack.
Yes, because Machia is "brainless" brute strength. And Momo is high IQ person.
So if you can overpowered Machia, you might able to ousmart/outplayed him.
I dont think they will able to stop Machia. Maybe they will able to stall Machia before someone strong came to "defeat" Machia.