Difference here is that we don't see people leaving at massive scale. Maybe it's to early. Anyway, I think chances are 50-50 twitter succeeds in re-launch. I wouldn't be surprised of any outcome. But I would be surprised to see something else explodes in popularity just because it's twitter alternative.
The issue is that if you wait until people start leaving it's too late. The bet here (and IMO it's a fair one) is that Twitter will continue to degrade as a service and eventually people will start leaving. If your alternative is up and running by then you've got a chance of capturing users.
