I hope the decision holds. But if it doesn’t, I expect that some state legislatures will be forced to strengthen their own explicit protections for the RKBA. Of course it may also be reasonable to expect that other states, and particularly cities, would see a reversal as license to increase restrictions or move from restriction to outright firearms prohibition. However, the laws in some of the more restrictive jurisdictions are currently so stringent that formal prohibition might not be much worse than what they have now, and severe new laws might energize opponents.
I think Steve Chapman is probably right that political trends mean that the DC court’s decision is more likely to cause problems for gun prohibitionists than for the RKBA.