if they used the same booster, say something like a Falcon 9, that was the cause of the disaster, anything using that booster would be put on hold until it was cleared. it just so happens the examples used very different systems, but that's not what you were referring to with your self assured declarative that just doesn't have as much weight as you want it to in modern launch systems.

I’m not sure that level of confidence is warranted. What’s going to happen with NASAs funding over the next few years? Or even SpaceX?

That literally isn’t true. A number of satellites had to be delayed or redesigned due to the Challenger disaster. Those satellites were planned to be launched on the Space Shuttle, and the Challenger disaster grounded the Space Shuttle for an extended period. And even when the Shuttle returned to flight, certain planned capabilities were cancelled as a result of Challenger, including West Coast launches (from Vandenberg) and the Shuttle-Centaur (an additional rocket stage designed to be carried in the Shuttle payload bay). Due to these changes, some orbits became inaccessible to the Space Shuttle, forcing those missions on to alternative launch vehicles. And switching the launch vehicle for a satellite isn’t simple, it requires redoing engineering analysis (every launch vehicle causes somewhat different stresses on the payload, so in the worst case the payload may actually require design changes to handle a different launch vehicle) and integration testing (the payload and launch vehicle need to talk to each other, and you don’t want to get that wrong, or else you can get failures like the first Boeing Starliner test flight.)

Even today, launch vehicles are shared between both crewed and uncrewed missions (Dragon uses Falcon 9, Starliner uses Atlas V), so a launch vehicle grounding due to a failure in one mission type absolutely can impact the other type too

> There’s no way that a disaster on a manned mission would affect a satellite launch. They share nothing in common.

It would definitely affect satellites, since the shuttle was a major satellite launch system. But even a deep space probe project like Voyager would be at risk, even though it seem directly related, because by affecting the political prestige of NASA, it effects everything that has to get funded at NASA – the politics of legislation are not bounded by rational direct impacts.

Except one thing: Politics.

Not just any foreword, a pretty big endorsement. You can borrow the book from the internet archive to read the full foreword, but here's the last bit:

    And in the end, it turns out that something will happen in 1982 that just may—
    No, no, read it for yourself. Read it carefully and you'll find it far more fascinating than the tale of any millionaire found stabbed in any library, locked or otherwise. And far more important, too especially if you live in California.

    ISAAC ASIMOV
    17 April 1974

Breaking that down: Voyager itself couldn't have reduced velocity, it had nowhere near enough reaction mass to do that. Hypothetically a spacecraft could but you might be talking about orders of magnitude more reaction mass. (Which means multiples more of the fuel to launch and accelerate that mass itself, which could quickly escalate beyond any chemical rocket capabilities.)

It also likely wasn't possible to get to Pluto on some future Pluto orbital pass. The limiting factor is likely that Voyager's incoming trajectory to Neptune was already too far beyond solar escape velocity to get into that narrow elliptical orbit you propose. (You'd have to slingshot so close to Neptune's center that you'd hit the planet instead.)

Designing from the beginning to come in slower to Neptune and adjust to encounter Pluto on some future Pluto orbital pass was probably possible, but yeah you might be talking about time scales of Pluto's entire orbit or even multiples of that. (We do similar things for inner solar system missions, like several encounters with Venus separated by multiple Venus-years, but that's on the order of single-digit years and not hundreds.)

The common answer to a lot of these outlandish slingshot questions is usually, yes it's eventually possible by orbital mechanics, but it gets so complicated and lengthy that you may as well just build another separate spacecraft instead. We talk about Voyager's grand tour alignment because it's captivating, but realistically if that hadn't happened we would have just done separate Jupiter-Uranus and Jupiter-Neptune missions instead.

The sun's motion relative to the galaxy doesn't matter for any of this - nothing else in the galaxy is remotely close enough to affect anything, the nearest star is still over 1000x Voyager's distance.