According to Not my theory but from some blog I read... i get information about Thatch being alive as theory.

He was the only one that was ultimately responsible Ace's death. more why because he taunted Blackbeard with the fruit...Blackbeard killed him for the fruit and ran...ace followed him and get captured and died. So the start was Thatch.

My Blog Friend was Saying he played Assassin creed and in the game there were two Blackbeard one was Edward teach and one was Edward Thatch. We all know ODA always takes inspiration from different things so what is bad in taking inspiration from a game.

I know there was his corpse lying on the floor but we have already seen Sabo dying but we have also seen him alive.

And also the corpse was only shown in anime may be it was just non cannon. It is just a wild guess coming to the mind.

Thatch was the first one on Moby dick to friend Ace. But what if he became jealous of Ace for being on top of him and getting more attention of Whitebeard.
It was never going to happen that ODA will show Teach killing Thatch without even asking him to give him fruit.

So what I think is that Thatch actually made everything up. We haven’t seen Thatch’s funereal or his grave. Blackbeard after doing that leaves a letter there and claiming he killed Thatch and stole his Devil Fruit. But actually he takes Thatch away with him.
Thatch is also a D. according to my theory above. He is the brother of Blackbeard, Marshall D. Thatch. In this way Oda gets in line with the exact kinda thing that happened in the history. What I think is that if he is alive right now then he is probably a commander or something big and bigger than Teach himself.