This is actually a pretty easy answer: since Republicans got elected, in large part, in saying they would repeal Obamacare. Republicans should do what they said they would do: Repeal Obamacare. Sorry Paul, your replacement plan is worse than just letting Obamacare die on its own.
Letting it die it hardly without risk (and there will be a lot of people hurt in the process) and there will be turmoil for years. The advantage in finishing it off is you at least allow insurance markets to recover. So if you are going to repeal, how do you do it? You have nominal Republicans like McCain and Collins who can't be trusted. You have to either throw out the filibuster or get around it.
But here is the intriguing part: That wily Ted Cruz has a plan for doing so. Not in grandstanding like Ted used to do, but instead working behind the scenes and engaging Vice President Pence?
Hey Paul Ryan, don't pull a Boehner...
Instapundit: Wait or use the Reid option, Voters will reward republicans if they do what they promised
Regular Right Guy: Paul Ryan and Obamacare-Lite
Hot Air: Tom Cotton and repealing Obamacare
American Thinker: Gutting Obamacare
Don Surber : Stifle it, Meatheads!
Daily Caller: GOP Singlepayer?
Wombat: Megan McArdle: Best Health Care Plan For Republicans? Wait