Abadon is an agent for Widmore the same way Alpert is/was an agent for Ben. I also don't think Ben has given up anything to Locke. He may have said that outside the cabin, but Ben is Ben and he hasn't yielded anything. My guess is that he is stepping down on a temporary basis so he can get revenge on Widmore for the death of Alex. That is his primary agenda at this point, everything else will lead to that goal and him landing in Tunisia in a winter parka (by the way, I think he has it on not because it was cold where he came from but because he wasn't sure where he would land). Somehow they knew to look for Locke when he was a child and Alpert found him first. Widmore didn't know who Locke was until much later, and then only because he fell from a building and didn't die (I think that's what caught their attention, and his survival against all odds as a premie caught Alperts attention, or at least built a case for him being the chosen one). Which leads back to Widmore and his search for the island....the Losties that get off the island are, in my opinion, the key for anyone who wants to find the island again (Ben or Widmore). Widmore will want them to go back to the island because the island wants them back and he can follow them there. Ben won't want them to go back until he has his revenge for Alex, at which point he can go back and take over again.