I'm sure Keyes didn't mess up anything. He learned his Lore-Ropes through and through, and checked everytime he forgot something. The biggest mistake he made must have been the U in Solsthiem, and it's not that big of a deal. Everything else on the entire universe has AT LEAST two names. I'm fairly sure some Dev wrote out a page and a half summary of what needed to to Happen, and Keyes just wrote 28something pages around it.
yes I'm pretty sure anything pertaining to any big changes in lore were already pre-determined by the writing staff. In fact, I rather like that all the cataclysmic stuff is happening in the novels as it sets the stage for the next TES. If all these things were happening during the game it would just be chaos, and it would be hard to find a single storyline to go with. Still, it's not going to stop people for blaming Keys for "ruining their lore" etc. some people just never pay attention. This isn't directed at anyone on here btw.