Thinks there's a possibilty that Megalodon still exists today?

For the most part, sharks aren't indiscriminate eaters. They eat what they are used to eating and unless you are in the Solomon Islands, that's not people.
If you want to swim in the ocean, bleeding like a stuck pig, or carrying around a bunch of newly speared fish, you are going to put yourself on the menu.
If you read the preface in the book "Jaws" he states that that shark has grown too large to feed itself through the normal food chain. This happens occasionally in OZ, where dogs begin to disappear long before the first human is taken.
We all fear being eaten alive, but in reality, it is much more dangerous to get into your car or on the school bus each morning, than it is to swim with most sharks.