A large economic majority of the community, you mean. Which gets to the heart of my largest misgiving about these networks: They are so transparently libertarian in striving to embody the Golden Rule ("He who has the gold makes the rules"). If a big actor makes a mistake that benefits 1,000 small actors, the little guys still get fucked.
If the US operated like this, Bill Gates would have ~500,000 more votes than the average American. You could argue that wealthy actors already exert outsize influence on our meatspace contract system, but I'd argue it's to a much lesser extent, and anyway, I don't see Ethereum offering much of an alternative. They don't even pretend to try to strike a balance between individual and community justice.
Economic majority is a copout, and it looks an awful lot like feudalism. As a little guy, I'm hesitant to hitch my wagon to that particular star.
So yes, it's possible your transactions will get reversed, but only if you've done something so horrendous that you've pissed off a large majority of the entire community, and in that case you'll likely still have your valid transaction on a working chain, it's just that a lot of people will have gone elsewhere.