Assuming all goes according to plan and the Senate passes whatever version of this thing gets to the floor on December 23, sometime early in January, Democrats from the Senate will meet with Democrats from the House to resolve any (and there are many) differences between the two versions.
This is where the mischief really happens.
In the movie biz there is a phrase for an actor flubbing a line in his 27th take, or dropping a glass in an otherwise perfect performance: "We'll fix it in post." Which means "We'll repair any errors in post-production.
The Congressional version of "We'll fix it in post" is: "We'll fix it in Conference."
The House-Senate conferees will meet in secret. They will craft a bill which looks nothing like what either chamber passed and they will each bring that version (known as a "Conference Report") back to their respective floors for a final vote.
This is a little complicated, but it is worth the typing. Conference Reports are privileged, meaning they can be brought up at any time and the motion to do so is not debatable. However, the Conference Report itself - in the Senate - is subject to filibuster and so needs 60 votes to pass.
Unless … It is a Conference Report presented as a "budget reconciliation bill" in which case 51 votes suffice. What is a "budget reconciliation bill?" That phrase is understood by only two people … and they don't agree.
Seriously, though. Because of the enormous budget implications of this legislation, it is quite likely that Harry Reid (D-Nev) will bring up the Conference Report under reconciliation. Republicans will scream bloody murder. Democrats will sheepishly withdraw to the cloak room.
The bill will pass the House and the Senate and, healthy or not, it will go to the President for his signature.