The black market is more typically looking for quick resale vs the extra work of data mining what's actually on the phone. YMMV.
Yes, there is some risk- but you have been without that phone for several years now with no issues to your ID, bank accounts, etc., correct? Nothing to see here folks.
So, first a bit of background:
About three years ago, I lost my iPhone 4 while out with friends in the city. I attempted to locate it via "Find My iPhone" with no luck (the battery was already dead when I lost it). I then set it on remote wipe and called my service provider (Verizon) to cancel my phone (I bought a new one shortly thereafter). I assumed that it was lost, as I never received any sort of email confirmation that it had connected to wifi and been wiped.
Now flash forward to a few days ago. I had nearly forgotten about it, and I was updating some information on my Macbook. Very foolishly, I accidentally removed the old, lost phone from my devices under "Find My iPhone" (it had never seemed to have connected to wifi in the space of three years and the "wipe" command remained pending).
I'm starting to worry about potential data theft in the future. I made sure to change my passwords for iCloud, Facebook and Gmail, just in case; the phone is also not in English (I live in the States), but in French, and has a four digit passcode. However, I find myself wondering (and worrying): what if it is found sometime in the future and someone manages to steal my information? My life was essentially on that phone (social security and student ID numbers, bank accounts and credit card information, etc.).
So, I guess my questions are: what are the chances that someone would be able to steal my data now, if they found this old iPhone 4? If the battery has been dead for all these years, I'd imagine they'd need to find a new battery for it, but would they be able to hack through my passcode still and get my personal data? Would there even be a black market for re-selling stolen iPhone 4's, considering it's obsolete and operating off of iOS 5 (or is it iPhone parts that thieves are after now)? Would it even be possible for someone to use it, with all of my passwords in place? The serial number and phone are still registered to me through Apple (and I think that the IMEI is blacklisted through Verizon), so wouldn't that prevent a thief from using my stolen iPhone as a cell phone with any carrier in the U.S. or re-selling it to someone, for that matter, with all my information? And, do black market resellers usually erase the data on stolen iPhones back to factory settings before selling them (one thief with my data is bad enough, the thought of multiple persons having access to my information is even more frightening)?
Sorry, I know there are a lot of questions here, but ever since accidentally removing the iPhone from "My Devices", I'm sort of freaking out about it.