We aren't going to sign Podolski to ONLY play when Van Persie is out (i.e. the roll Chamakh has played this season - bugger all!).
If we get Podolski, I would expect to see a lot of him up the left, as well as taking the pressure off Robin up the middle (i.e. covering for injury, and allowing to come off after 70 minutes every now and then, and maybe even resting him). With that in mind, and Theo, Gervinho, Chamberlain and maybe Miyaichi coming back as well, I'd be surprised to see space for Dempsey open up anywhere.