Well, King has said that he based Roland in part on Eastwood, so if Eastwood was born later, there very well may not be a Roland (at least in the way we know him). Isn't circular logic wonderful?
Yes it's tragic, but a DT movie would be so screwed up by the process of moving it to film It's best left unfilmed. I still need to read book 7, just no time for reading lately!
There's a couple of times the Eastwood/Roland comparison is explictly made in the books. Eddie makes the comparision when he and Roland first meet face to face, I think.
A DT movie would be bad. BUT a series/mini-series on HBO or something could get it done, I think, especially given how the series ends:
Spoiler from book 7:
The last episode could end with the beginning of the first episode, except that Roland wears the Horn.