I'm sure that not every rabbi holds of the 6,000 year thing. Because after all, there are many Orthodox rabbis who do not believe the buba maiseh that the world is only 6,000 years old (there is not a single source for that). So it's only natural that that time is also not the "end of the world" Or whatever. That 6,000 years thing can be metaphor or mashul. It is aggada afterall. But anyway, hopefully redemption will come even sooner than that date. If it doesn't come we keep trying, that's all. Only unreasonable/illogical people will lose hope if it doesn't come by a certain date.