Some people have found that one or more BF merchants can shift locations, either occasionally or each time they enter the BF. If a merchant moves into another object (tree, tent, etc) they will become invisible.
Since you already re-enter the BF repeatedly, waiting for him to come out the other side may take awhile. You could try alt-tabbing out of the game and back, which can also sometimes shift NPC positions. These locations can also be edited.
Teleporting anywhere (via hex editor) - details on BF merchant teleporting are in two replies (the second may be a bit easier to understand if you are not familiar with hex editing)
