The opinion stands until the federal government formally appeals the holding where an appellate court takes the appeal and then rules contrary to the unconstitutional opinion against OBotcare.
If the higher courts refuses to hear the case, it is tantamount to stare decisis as they are letting the lower court ruling stand.
However under our court system, the issue could never end, if people continually challenge the law even after the Supreme Court have ruled on the case. In theory nothing is totally immune from being overturned.
In this interest of factual accuracy, that is not entirely true. If the Court denies certiorari, then no binding precedent is established beyond the precedent that is established in the Circuit that the case originated.
In this particular case, we're talking about a facial challenge to the constitutionality of a federal statute. Generally speaking, that is a VERY high threshold to reach, especially since the Court decided US v. Solerno back in the late 80's. As a purely practical matter, given the importance and rarity of such cases, it's HIGHLY unlikely that if this challenge prevails on appeal (and thus far, both Hudson and Vinson found merit to the challenge), that it wouldn't be heard by the Court. Remember, you only need four to hear the case, not five.
Modification or not, I asked that you provide an authoritative citation or at least an example where this occurred. In contrast, I can provide a large number of counter-examples where it was not true. You can start with this list:
ACTS OF CONGRESS HELD UNCONSTITUTIONAL
Not all of those will apply. In some of them, the district court held something unconstitutional, but the circuit court disagreed, and then the Supreme Court agreed (with the district court). In others, it was the district court that got it wrong first, and the circuit court was the first to agree that it was unconstitutional.
A US district court decision does not automatically change the law in the entire US. It certainly calls things into question, but it's not even a binding precedent outside that district.
Revoking a law nationwide requires a decision by the Supreme Court, although you can achieve the same thing with a Circuit Court case that becomes precedent nationwide. That's why the Supreme Court rarely takes a case unless the Circuit Courts disagree -- there's no need.