Question, what would it take to recover that kind of knowledge? Would you need to interview the people who built the rockets to get the "tricks of the trade" and or the original data and blueprints in order to rebuild the industry?
Depending on how long you've gone since you had the capability, you might well need to start pretty much from scratch. If you aren't in an industry with a lot of "tribal knowledge," you'd be amazed at just how far short of the mark you get even with complete blueprints.
Let's say you have the complete blueprints for, say, the Thunderchild Inter Planetary Ballistic Missile. The USSF built a thousand of them thirty years ago, tested the hell out of 'em, and they worked beautifully. But the last time they were in production was twenty years ago, and the last time they came in for a complete refurb and overhaul was fifteen years ago. Now you need to refub 'em again. Alright, fine. You have the prints and the process instructions.
Step one says to remove the existing solid propellant from the case. Last time, they used a mechanical, robotic "excavator" to scoop out the propellant. But that facility was shut down a decade ago because of environmental complaints from the yuppies who decided to move into the area. "No problem" you say, you simply ship them to your *new* facility that uses high-velocity water jets to wash out the propellant. The water jets cut through the propellant like a hot knife through butter, but doesn't damage the case. Great! That gets rid of the sparking issue everyone was so freaked out about with the metallic cutter heads with the old system. So, you put the first Thunderchild motor into the water washout setup, turn it on and... BLAM!
The instant the water jet touches the propellant from the very first motor, it detonates. Entertainingly, the other fifty Thunderchild motors were stored within the blast radius of the first, and they all sympathetically detonate, turnign your sparklingly new facility into so much confetti. What the hell happened?
Ooops. Turns out that the last time through the system, the propellant used had the normal iron oxide burn rate modifier replaced with ferrocene. Ferrocene has all kinds of nifty advantages. Sadly, ferrocene has the unfortunate habit of migrating over time out of the propellant, and gathering on exposed surfaces. So when the supersonic waterjet hit ther surface, it hit a patch of propellant supersaturated with burn rate modifier... which modified the burn rate to over the speed of sound, turning that patch of propellant into a high explosive. Neato! Too bad that the notification that the propellant had been changed was a minor notation that nobody really noticed, buried fifty-eight pages into the process paperwork that you didn't really read, and couldn't have anyway due to it being a faded fifth-generation photocopy. And of course, the post-it note that said "don't use a supersonic waterjet, makes propellant go FOOM" fell out of the folder during the paperwork handoff. And the guy who wrote it got run over by a giant radioactive rubber Jimmycarterbot in that big foodriot at the UberWalMart three years back....
This may sound a tad flippant, but it's actually based on an actual incident.
There are a lot of bits and pieces of rocket motors that don't neatly fit into the blueprints. A notation that some particular widget is Part Number XYZ from FailCo doesn't really help much since FailCo got bought out by Predatory Lending Practices, Inc, which turned the FailCo division into a toy manufacturing division, and then sold it off for parts. And I've seen more than a few process instructions that called for doing something that was not defined within the process instructions... often this meant using some chemical that was no long approved (generally due to environmental concerns). And I was even involved with the re-creation of a substance that was *physically* *impossible* to manufacture, as described.
If you get out of the IBM business, chances are *really* good that if you want to get back into it, your best bet is to take the ICBMs you actually have out into the desert and blow 'em straight to hell with a few tons of high explosive and napalm. And then start from scratch.