that would have disintegrated in a gas giant (Bespin) within seconds of falling into it at the climax of ESB
You’ve made an unsubstantiated assumption that it fell out of the garbage chute to begin with.
I don’t get why so many people insist that Luke’s lightsaber must have fallen into Bespin? There are so many possibilities as to what could have happened to it.
It’s not impossible that lost objects could be dumped into the gas giant, but simply hitting a floor at the bottom or being sucked into one those tubes that Luke fell into are equally probable. According to TFA they obviously went with one of the latter (as did Legends I might add). Why is this such a big deal to some people?