I mean after patch 1.9.

no. you can skip the guild all together and just talk to the guy running the bar in the ragged flagon.

You might just be able to go right into the sewers and find Esburn on your own.

I know people seem to to think you need to join the thieves guild but you don't.

and dirge is killable now? sweet. His "Don't mess with me" crap got stale really quick and I'd like to see just how tough he really is.

I ignored the people in the flagon last time I did it, and went for esbern on my own, it worked.

Guys, I wasn't asking if you have to deal with Brynjolf in order to get to Esbern.

Some say that killing Dirge causes a glitch in the Cornered Rat quest. I'd like to know if that's still true with all patches and everything.

Well. I'm confused as to what part he even plays?

If an actor's alias is non-optional, and does not allow for the actor to be dead, then any aliases containing that actor cannot fill, and any quests containing those aliases cannot start.

Dirge's alias in MQ202 in Update.esm is flagged to allow dead actors, so no, killing Dirge will not impede your progress in that quest.