That's not how it's worked in the past[1]. I was explicitly going by CSAs instead of states to avoid some of those issues[2].
From personal experience, I'd say it's better to live in a non-nuclear[3] country, because the local economy can be directed to positive sum consumer and export goods instead of negative sum MAD. So if Colorado were to leave (with our already unlikely assumptions, yet more unlikely due to network[4] effects) I would recommend only doing so politically, allowing the US to continue with basing rights (following the model of the Rest Of The World).
and then there's the small matter of who takes responsibility for a large national debt...
[1] indeed, ever since the unpleasantries of the 1860s I believe it's US military doctrine to base people in regions other than the one they're from.
[2] specifically, I believe the US would commence hostilities well before losing Kitsap and San Diego, let alone Pearl Harbor (because as long as we're in cloud cuckoo land, I'd bet hawaiians, no matter their attitude towards the mainland or fondness for Las Vegas, would prefer being stuck with the west coast than with anyone east of Stockton, and they don't have any economic argument for complete independence.)
[3] as others in the thread have noted, there is a non-negligible chance that third parties would be willing to provide an umbrella. My democracy has managed to survive the last 500 years with a policy of "we're no threat to you unless you cross our border" and indeed we even apologised to the last country we invaded (they replied no hard feelings).
[4] with navigable waterways (and some credible way to deal with harbour mining and general naval interdiction?) money will get one through times of no food better than food will get one through times of no money. Airlifts, as Qatar has discovered, are expensive.
Edit: found GDP by CSA, population was a good proxy (but inland goes up to 25% of top 20)
https://apps.bea.gov/iTable/drilldown.cfm?reqid=70&stepnum=4...
inland CSAs
7 Dallas-Fort Worth 0,5 T
11 Atlanta--Athens-Clarke County--Sandy Springs 0,4 T
15 Denver-Aurora 0,3 T
16 Phoenix-Mesa 0,3 T
20 Charlotte-Concord 0,2 T
so top 15 CSAs with navigable access only represent about 11 T of GDP, and if they (and I doubt the following would change much if we added coastal CSA's below the top 20) went their own ways the remaining US would presumably still be globally in 2nd place, with an economy roughly double that of the japanese.