Lucky Bamboo is a dracaena not a real bamboo.

leaf buds can grow at any knot; submerging leaves won't kill them immediately but bacteria will rot them eventually making a brown mess so it's best to cut the bud off if you want to keep the stem as-is & that part underwater

alternately you can chop the stem above the leaf bud and reroot the top part... top stem won't (very rarely) grow taller/new segments since its growing tip has been amputated & capped by the nursery. Could try some rooting powder/gel but healthy dracaena will usually reroot itself in water within a few weeks

bottom part with the leaf bud... you can trim off the old roots, scrape off a stripe of green layer off the stem opposite the leaf bud then plant it horizontally into a cup of sand & water. Stem will root, the leaf bud will upright itself and grow you a new stem :)

However... dracaena is slow growing so be warned it's a long project. And whenever there are open wounds bacteria can/will takeover & kill everything from toxicity... sterilise instruments/water/growmedia before surgery to lessen risk but it still relies on a lot of luck.