In those cases, Proposition 8 ended up being held to remain invalidated (Hollingsworth v. Perry) and the so-called Defense of Marriage Act (DOMA) was struck down (United States v. Windsor).
Today's case was Obergefell v Hodges and you should read the always excellent SCOTUS blog for complete coverage and a plain-english explanation of what happened. Apparently, no one is very sure of what the final decision will be. That really, can be considered something of a win for the heterosexual supremacists because they have spent the last 18 months or so losing literally dozens of cases before federal judges who have been striking down bans on same-sex marriage using the United States Constitution and the reasoning contained in Windsor.
If the Court does decide that there is NOT a fundamental right to marry for same-sex couples *and* that states do not have to be forced to recognize marriages from one state that could not be performed in their state, then the Washington Post has a good map and explanation of what the state of play could be.
Only 11 states have enacted marriage equality through "majoritarian democratic" processes so far, so it would mean that there would be battles going on in 39 different states to change the law. This would potentially include California, where Proposition 8 is not the law of the land due to a District Court decision that would no longer be valid if the Supreme Court issues a ruling that changes the legal landscape. You can bet that heterosexual supremacists would start litigating to have Proposition 8 re-instated and LGBT activists would rush to collect signatures to have a 2016 vote on the question.
The 21 states whose marriage laws have been struck down by lower federal courts and where couples have been getting married legally would suddenly have their marriages thrown into limbo (although it is more likely than not those marriages would be deemed valid, but it might take another Supreme Court case to resolve that issue).
Let's hope the Justices do the right thing and realize that there is no harm to opposite-sex couples when same-sex couples are allowed to marry.
Hat/tip to Scotus Blog and Joe.My.God