About the only thing Guardians struggle with in heroic 25man is circumventing intended mechanics or avoiding tank switching. While other tanks have active mitigation tools that can deal with higher-than-intended tank-killer mechanics (typically stuff revolving around debuffs), Guardians take most of it to the face and have to use major cooldowns to deal with it up to a certain limit. That isn't to say you can't do things like solo-tank heroic Malkorok as a Guardian, it's just not as easy as it is for other tank classes.
Be that as it may, if you die on heroic 25man as Guardian, you were either 1-shot by something you shouldn't have been hit with or you're purposefully wiping... we're pretty resilient. The beauty of FR is that it almost removes the requirement of a healer once your Vengeance is high enough.