The DM behind the siege posted a "reveal" with a lot of OOC info to aid players understanding events.
Subject: 1351 Metaplot Ending and reveal
Why they assaulted the city, there could be several theories about. I would suggest that if you want to know, that you go around the server and ask other people ICly. It is a finished plotline by the way but people have been very happy to share at least the basic information. There are IC rumour threads in the Elfsong since last year but these have been unstickied so you would have to dig them out.
I think on this server, what player characters do can matter. The DMs are reluctant to use characters such as Elminster or any other powerful one to save the world whenever there is a crisis. It is pretty much up to player characters to think of ideas and try to make things happen.
Player characters came up with the idea to use sun cannons and some other things at the siege. There were lots of NPCs but they were never really seen. There were several Lords' Alliance soldiers from all over and also Greyfox tribe members as well as militia 'pups' in training. It is difficult to have fights with PCs, allied NPCs and hostile NPCs in an event where there is already much lag. But I still believe negotiating for these allies mattered in such way as to how long the walls would hold, how the defence lines were and so on... but it was not the NPCs who shone but the player characters.
Some characters did join the NPC's side, or at least aided them. Read the "reveal"!
Oh, I saw that the Dukes called forth some charge or whatever in the siege but I suspect the DM added it in afterwards cause I did not see any of the Dukes?

Nor do we know what happened to Lady Alustriel and her flying carriage...? I saw one post about it and I guess she was forgotten!
While what player characters do can matter... I feel the DM team is quite torn on exactly how much player characters themselves can matter. Now and then there is a discussion about some people and some DMs viewing all player characters as half their actual level (which I disagree with, cause "play what's on your character sheet" and how do I explain an epic spell, even a 9th lvl spell if I am supposed to play as a lvl 15 char?
No do not answer please. Make a new thread if you must, veterans.).
Some DMs also do not want player characters to be distinguishable from the masses, which I also disagree with... because it is possible to do deeds on this server which really singles your character out. Or your character can simply gain a reputation... but it seems like, for the most part, reputation only matters between player characters. I would be baffled if an NPC in Baldur's Gate had not at least heard of my character... because she is rather infamous *twitch* but also very good as a performer on stage where the Dukes even attend
(and she has ungodly charisma).
So you can experience different levels of how your character is perceived depending on the DM really. But NPCs saving the day... nah, not really. They are just lazy and ask adventurers to do it most of the time
I have only seen Elminster once during the time I have been playing, he told some story or something at a Candlekeep fair. I cannot even remember what it was... I have seen Fzoul Chembryl once and he basically sat on a throne and told the Zhentarim that failure was not an option. ...I have probably seen more deity avatars than important lore NPCs. So you can worry more about deity avatars stealing your thunder rather than important NPCs.
Lastly, I would recommend you to make a character if you have not already. Best way to understand and experience the game is to play it. You will soon discover it is very different from a PnP game and while the base is in FR lore, there is a fair deal of server lore as well as deviations. And of course, the play style differs. Majority of the time, you do not have a DM following your every move.