From the moment I heard Leta's story I thought: what if Credence's mom was also a witch, since Credence is a wizard, and because of that able to have saved Corvus? Leta only saw the boat crash, she didn't actually see the image of her Boggart, that's only what she assumes happened.
Yusuf made an Unbreakable Vow that he would kill Corvus. If Corvus was already dead, Yusuf would have failed, shouldn't Yusuf be dead as well then? Or does this mean Corvus can't be dead yet?
The film implies very heavily that Corvus died in the sinking of the liner. Firstly, we have Leta's first hand experience of the event who seems pretty confident the baby and mother never resurfaced and that they drowned. The official screenplay also refers to "drowning baby" a couple of times with no mention of him being saved. Lastly, we have the family tree which shows Corvus' label withering and dying implying he is dead according to the family tree.
SCENE 109
EXT. LIFEBOAT—1901—NIGHTCHILD LETA, IRMA, and BABY CREDENCE are in one boat, CREDENCE’S AUNT and BABY CORVUS in another.
A huge wave is approaching. CHILD LETA watches as the lifeboat bearing CREDENCE’S AUNT and BABY CORVUS is overturned.
CLOSE ON THE SURFACE OF THE WATER. A few survivors reappear, including CREDENCE’S AUNT, but not BABY CORVUS... CREDENCE’S AUNT pulls off her life jacket so she can dive too...
She does not reemerge. We close in through the surface of the water, past the drowning woman, and see the dark shape of a drowning baby trailing bubbles of magical light as he sinks... and his figure becomes...
SCENE 110
INT. LESTRANGE MAUSOLEUM—NIGHT...the drowning baby falling through sea-green light, hanging in the air in the mausoleum. LETA has conjured it. It has haunted her all her life and now she shows it to them.
The orchid representing LETA on the Lestrange family tree twists around the branch labeled CORVUS LESTRANGE until the leaves wither and die.
Fantastic Beasts: The Crimes of Grindelwald - The Official Screenplay
Of course with nothing explicit such as seeing the dead baby this could change but I highly doubt it.
FWIW though Kama's Unbreakable Vow was to "Kill the person Lestrange loves best in the world" and Corvus was not born at that moment which implies, such is love, that it changes. Therefore, even with Corvus dead the Vow would carry on to the next thing Lestrange loves the most in this world.
SCENE 101
INT. KAMA MANSION—1896—NIGHT[...]
KAMA: The news of her death drove my father insane. With his dying breath, my father charged me to seek revenge. (determined) Kill the person Lestrange loves best in the world... I thought at first it would be easy... he had only one close relative... you. But—
LETA: Say it...
KAMA: ...he never loved you.
SCENE 103
INT. LESTRANGE MANOR, BEDROOM—1901—DAYWe reenter the story to find LESTRANGE SR. with a new, blond wife.
KAMA (V.O.): He remarried not three months after her death. He loved her no more than he had loved you... But then...
IRMA takes the BABY BOY who has just been born, and passes him to LESTRANGE SR., who is delighted.
KAMA (V.O.): ...his son, Corvus, was born at last. And that man who had never known love was filled with it...
Fantastic Beasts: The Crimes of Grindelwald - The Official Screenplay
