WARNING: The following article contains spoilers from Fantastic Four #41, on sale now.
The Fantastic Four have seen all sorts of things in their long and storied history, but recent events and the history surrounding the Reckoning War are redefining what they thought they knew about the universe. Their new enemy is more advanced, outnumbers them, and has absolutely no mercy and in Fantastic Four #41 (by Dan Slott, Rachael Stott, Erick Arciniega, VC's Joe Caramagna) things became much more dangerous when one of their members, Rapture, destroyed the Thing's vibranium wedding sword with an energy blade.
The parallels to a lightsaber are obvious, but this brings up history's examples of what can destroy vibranium as well as a comparison to what can block a lightsaber.
Vibranium is one of the strongest materials in the Marvel Universe. Despite this lofty title, it is not indestructible, there have been many instances over the years of vibranium weapons being broken. The most obvious example of what could do such a thing would be another weapon of a similar or stronger substance, weapons also made from vibranium, adamantium, or uru are capable of damaging, even breaking something made of vibranium.
There are other methods of course, such as brute strength. Two individuals have managed to break Captain America's vibranium shield. Thanos was the first, though at the time he was empowered by infinity gauntlet, so it is debatable whether it was Thanos' brute strength that shattered the shield or if the gauntlet enabled him to do so. Despite this, there is an excellent example of a vibranium weapon being broken with physical might. The Serpent, the god of fear, managed to shatter the shield as if it were glass, with seemingly no effort. So brute force is one way to destroy vibranium, but only if one possesses the strength of a god or nearly one.
Now there seems to be a new way added to the list. Rapture's weapon has not been explored in too much detail, but given what is known about the Reckoning, it makes sense that they would possess technology capable of fending off vibranium based weaponry. With their technology being a gift from the Watchers that they in turn abused, the Reckoning stands as the most technologically advanced race in the known and unknown universe right now. Rapture even expressed familiarity with the metal, so it's highly likely this weapon was crafted with vibranium's capabilities in mind.
It's also a fun inverse of the recent addition to Star Wars lore about beskar steel, a special metal the Mandalorians use for their armor. It is capable of protecting them from intense blasterfire and even lightsaber strikes. In this scenario though, Rapture's "lightsaber" is more than capable of cutting through the Thing's "beskar".
This isn't the only substance capable of blocking a lightsaber though. Both Stars Wars Canon and Legends is full of materials capable of blocking the plasma of a lightsaber. Zillo beast hide is a prime example from the canon material, perhaps even the first real substance shown to be capable of such within the new lore. As for Legends, the best known example is cortosis, a rare metal often used as armor or shielding against lightsaber wielding foes, but one that is incredibly difficult to acquire.