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Lightsabers are more than just light, they're concentrated energy. The name just sounds neat.
And to your question, that's an incredibly vast amount of energy compacted there, the superlaser alone is already unbelievably powerful. I suppose so, Luke didn't seem to have much trouble deflecting the blasts from the speeder bikes, and I'm pretty sure they're stronger than normal blasters.
I'd say so, but whatever it hit afterwards would explode taking the planet with it.
Luke has been seen deflecting the cannonfire of AT-AT cannons in Dark Empire, and I believe those are significantly more powerful than most things in the Star Wars arsenal.
But if we're going to say that the Death Star beam has been compacted to the size of an AT-AT blast, then yeah, that amount of energy might shut off the lightsaber due to the strain.