In another thread, it was mentioned that UA has retired 21 ERJ135/145 this year. It will take another 25 years to retire all of them at this speed
As of April, they were showing a plan to remove 9 135's and 34 145's from service in '14. They will be likely be accelerating the 145 retirements faster than the fleet plan indicates. 43 ERJ's is ~15% of that fleet, so that's ~6 years at that rate.
I don't think anyone expects them to get rid of their entire regional fleet. However, a massive downsizing (~50-60% of the 145/CR2 fleet) would make a lot of people, myself included, happier about their position.
The Dash 8 fleet and the 120's serve quite a niche, and has a much lower fuel operating cost than jets. That and they actually serve a regional purpose, I think they make sense.
The CR7 and E-jets offer the potential to have a decent onboard experience for a 90 minute flight (though the slimline rocks in the CR7 are quite awful). UA could choose to improve the onboard service on those if they chose to be competitive, but I see no indication of that.