You missed out the small but very significant detail of being able to create your own world state in the Keep.
So your theory does not really hold water.
Personally, I would be glad if the Warden does not appear at all to allow people with mommy issues to finally move on.
Except how are Bioware supposed to indicate that someone's presence is conditional based on world state within a trailer, without showing us the same scene several times with multiple characters?
The idea that the Warden not appearing in the trailer is because in the world state of the scene we're watching from that trailer, the Warden might be dead, seems to make a lot of sense to me.
Your argument that the Warden's not in the trailer because we've got the Keep to have them alive, is like suggesting that we should ignore everything we saw in the demo footage of Redcliffe castle, because the Inquisitor in that case was female and Qunari, whereas we have the CC to create whatever race and gender Inquisitor we wish?
I suspect that if the Warden does appear, it's going to be kept as a surprise and they're not going to announce it in a trailer.
(Although, I'm just as apathetic to seeing them again as you are. The Warden was awesome, but let it go people! Hawke's appearance excites me, but I'm filled with just as much dread that their appearing could lead them to being killed off unceremoniously, which was a shame because I really liked that character. I'd rather the Warden and Hawke just stay as background characters and if they do appear, have very little impact on the overall plot)