There are a few mods out there for dispatching the Thieves Guild - but none of them have that great a level of immersion as one would hope, and I feel that something slightly more elaborate is needed. Basically - there have been found in someone in Riften's house certain pamphlets regarding the Thieves Guild (I can't remember who's) and they could very well be from an unused "Destroy the Thieves Guild" Quest.

Basically - my idea is such:

Mjoll contacts you, telling you that she has a plan to rid Riften of the Thieves Guild once and for all - and she tells you to go and talk to the citizen that has the pamphlets. Upon talking to them, they give you the pamphlets and tell you to give them to the other store owners in Riften. You go about doing this - and give them each a leaflet. After giving them all out, you're confronted with a Corrupt Guard who knows what you've been up to, and arrests you. However, rather than throwing you in jail, he hands you and Mjoll over top the guild - and they incarcerate you. The next part of the quest is to escape - not sure how this part'd be done, but you don't actually run into any members of the Guild. After escaping, you agree with Mjoll that the plan is too long winded and that a new change of plan is in order. She says she'll go about telling the citizens, and that you should meet her outside the Ratway at midnight. When you get there, you find that the other citizens are outside, and that they're planning to storm the Ratway. You do so - and there's a big fight between the Riften...ites... and the Guild, and after you win, you have to go to the Jarl to tell them that the Guild is no more.

This could lead on to a separate quest that's dependent on your point in the Civil War Questline, involving either exiling Maven or ousting her as Jarl - however, this would probably be an even bigger undertaking, and would take a lot of work. However, with a lot of people thinking behind it, it could theoretically be quite straightforward.

However, while all these ideas are well and good on paper... I have absolutely no modding skill whatsoever. So I thought that perhaps I should suggest it to you guys here. It's just an idea - but I could actually see it becoming quite something, if people were willing to put the work in.