When I read "remains of the castle", I thought there will be some damage inside but that'd be about it and the basic structure will stay so that it can be repaired later. Apart from the furniture, there is not a single wooden or brick structure inside the castle since it is built by only using stone and stone is not exactly known for its high flammability. You cant wipe a castle with a medieval crowd, that is not how it works. In fact, destroying a stone castle is so hard that armies used to make the castles they conquered their new headquarters. And also, search for burned down castles on the web, you will see that all of them are still standing today, even the ones burned down a millennium ago.
And for the 12 year old item a Seer placed comment, Ultima Online is "our second home" as Lord British put it in September 23, 1997; so it is more than natural to feel upset when someone wipes a part of it. You might not care, but we do, show some respect.
Well I can't speak for for any shard other than Chesapeake where I reside, but...
The whole point of the shards to begin with is we each have the same world but our own histories unfolding. On Chesapeake, kegs of alchemy devastation potion were stolen and used to destroy the castle. This mixture was a formula researched and developed by Balandar the Archmage(EM RPC) on our shard to clear mountain passes and cave entrances. So at least on Chesapeake, it is very likely there is no castle remaining.
In regards to shard histories. We have a lot of incredible players on Chesapeake and I'm sure on other shards, who spend a great deal of time, gold, and energy in preserving our histories. It may be spending many hours creating a well decorated museum, writing books, maintaining a library, hunting down and spending large amounts of gold and RL $$ to bring back historical artifacts that have been traded off a shard, or spending countless hours designing web articles, maps, etc...
Like any society, sometimes it requires the community to take an interest in observing, preserving and protect their own histories. In the real world histories are often destroyed, decay, lost, and forgotten.
The above is not meant in any way to be a slam against anyone, it is simply to point out that different shards may have completely different experiences.