Depends completely on who ends up leading them and the policies that they UCP decides to focus on. If the leader and the UCP's policies are not progressive enough they will definitely bleed red tory votes to the AB NDP and AB Party.Their path to victory is appealing to progressive voters. If they fail to appeal to progressive Albertans they will lose the 2019 provincial election possibly in another landslide. Right now they aren't really saying anything or doing anything that makes me think they are guaranteed to win under the UCP banner in 2019.
Danielle smith wrote a piece on global related to the annoucement of the UCP I agree with.
http://globalnews.ca/news/3462378/danielle-smith-conservative-merger-no-guarantee-of-victory/
Every election, even during the later years of Klein, was won by appealing to the centrist voters. Klein himself had to massively increase spending during his final term because he had to show 'dividends' from the cutbacks in the mid-90s.
Stelmach and Redford both won on centrist agendas. Whether they governed from that centrist agenda is another question altogether, of course.