Find My iPhone "Erase Pending" & No Passcode My sister just got her iPhone 6S stolen. She somehow managed to ignore my advice to apply a passcode. We put the phone into "erase mode" right after we noticed it was gone. 

Theoretically speaking, what info does the thief have access to? I know the phone will enter erase mode as soon as it connects to a network, but assuming it doesn't, and assuming the thief does not elect to wipe it himself, what kind of information can he access?
First, be sure to go to this Apple Support page and follow the instruction for what to do if your iOS device is lost or stolen.  Your options will be limited, as will your ability to control the 'damage' the person with the iPhone can do, because it wasn't protected.


  What if your device is off or offline?
  
  If your missing device is off or offline, you can still put it in Lost Mode, lock it, or remotely erase it. The next time your device is online, these actions will take effect. If you remove the device from your account while it's offline, any pending actions for the device will be cancelled.


The thief can simply not allow the iPhone to access the internet and then do whatever they want with the data on it.  They will have access to any app that's not password/passcode/fingerprint protected.

I would recommend you change the password, ASAP, for any app/site that is accessible on the iPhone.