take a look at their debt profile. if leh goes into chapter 7 why would anyone keep money in MER knowing they might get into a mess that would take forever to get out of. $72b in deposits alone, this is ultra short-term debt as I understand it. I dont think MER has enough good assets to pledge at the discount window to handle a run http://ir.ml.com/debtprofile.cfm
looks like roubini agrees with this "If Lehman collapses expect a run on all of the other broker dealers and the collapse of the shadow banking system" http://www.rgemonitor.com/blog/roub...and_the_collapse_of_the_shadow_banking_system
The first link has data from June 2008. Do you know how their profile has changed since? It's true though, MER is definitely not in great shape, a collapse of LEH would probably not bode well for the others (good short opportunities? )