Most of the scientists and researches that megalodon shark happened to got extinct about 1.2 million to 20 million years ago. There has been no proof that megalodon shark is alive.
Some scientists believe that megalodon might have changed it’s DNA with years and were most likely to convert into great white shark of today which closely resemble historical megalodon shark. Most of the information about these sharks we know today is derived by studying the fossil remains of megalodon mostly teeths as they happen to have sustained and can be found in good condition.
However it is thought that still about 60% of the oceans is still undiscovered so there is chance that megalodon shark might have gone into deep oceans and may show up someday but it is very very rare chance as these sharks were highly mobile and if they were alive they would surely have shown up up till now!!