The problem I'm seeing for the GOP is they have to play to two different groups here and try to thread the needle to get something to work.
I'm not talking about the Ryan wing vs. the Freedom Caucus ... it's the Senate vs. the House.
The House is split, indeed, and its worried for separate reasons (Ryan and friends know a failure essentially puts them in lame-duck status; Freedom Caucus knows that if they buckle to Ryan now, he has them by the balls from now on and their influence is diminished). But House districts are still by and large gerrymandered and without a Trump-led primary, many of them would likely be safe if it passes a House vote.
The Senate, meanwhile ... those who are Republicans from blue or purple states, or states where the ACA extended health insurance to millions that didn't have it before (and won't have it ever again if AHCA becomes law), have to be worried if this blows up. Not for 2018, but for 2020, when 22 of them will be up for re-election and a pissed off electorate wanting blood could send many of them packing if there's an especially strong wave election (Cory Gardner, Joni Ernst, Susan Collins, Thom Tillis, and hell if it gets the coal miners angry enough, even McConnell could be vulnerable). They have more legitimate concerns about this going haywire and causing issues when they're at their most vulnerable in 2020, and they'd likely rather have a failed ACA to use as a cudgel in 2018 to drive people to vote Dems out of office en masse.
The problem for the Senate is that the House can't afford to wait. They need this passed now because they have been making promises to do this for so long that their constituents might start getting tired of waiting. And Paul Ryan knows if he can't get the job done on this ... POTUS just might turn his Twitter guns on him next.