Re: For the boffin's sake I hope they have a backup plan.
FH has yet to fly, and has yet to be integrated - but the side boosters of FH have flown many times, and the engines and tankage of the FH core are a proven design.
- Heck, the demo launch has already flown 0.6 times, if you squint.
The main part of FH that's untested is the integration. They've never tried to run and balance three cores simultaneously.
SLS on the other hand, is using new everything except the liquid engines. While it's all based on earlier designs, there's a lot of pretty significant changes. They've only done static fire tests, so can't be as confident.
FH is very likely to fly in Q4 2017/Q1 2018, and SpaceX have long proven they have the manufacturing capacity to attempt a paying payload launch very rapidly - STP-2 may well be within a month of the demo flight, unless they find significant anomalies.
I'm pretty sure that the SLS Block 1/1B EM-1 and EC will happen either way, because most of the cost of launch has already been paid and it's unlikely to be possible to reintegrate the EC payload into FH. However I suspect that many other SLS missions will be moved to FH.
The ULA must be bricking it. If EM-1 is delayed much more - or worse, fails...