Supplemental to Karlson's excellent answer, I want to add a few points about where the PPACA can pose problems for expats. While it is true that you do not need to worry about the individual mandate while living abroad (according to the rules in his answer), there are particularly nasty implications of this mandate for expats anyway and being aware of these is the first step to avoiding problems.
If you are an expat married to a non-US citizen, then when you return to the US, the individual mandate requirements apply to you and to your spouse (and children if applicable), but non-citizens are not eligible for Medicaid for the first five years of residency, and so while subsidies are available down to the poverty line (but not below, meaning if you are under the poverty line you get no subsidies), if you find yourself unemployed during that 5 year period, it could be painful financially and you will need to prepare for extra paperwork/justifications to the IRS for a financial hardship exception. This is particularly problematic of course if you are or intend to be self-employed during that five year period because the normal assurances of the PPACA do not fully apply to you.
My recommendation is that if you are at some point preparing to move back to the US with a family with non-citizen members, that you do not expect to be self-employed initially (if that is a goal), and that you find out exactly what the IRS wants to show a financial hardship in your case (these rules are of course subject to change as the authority to make financial hardship rules was delegated to the IRS).