If things get bad for MS (and I don't think they are). They may release DX10 for non-vista systems. Vista has very bad support and I don't think that's going to correct itself in a timely fashion, not until some serious service packs come out.
The industry won't undo it's history with DX overnight. It will need some time to say, "Yes, there is need for change." And then it will take some time for the competition to "get their asses in gear."
As a member of the indie games development community I can tell you that the choice between DX vs cross-platform solutions can be tough. That said the majority of games released are for windows. The question really should be as Soleron indicated, "When will Microsoft's stranglehold loosen?" When MS really starts to lose influence then we may see a strong move away from DX.
