Howard the Duck made his Marvel Cinematic Universe debut in 2014's Guardians of the Galaxy, and later made cameo appearances in that movie's sequel and Avengers: Endgame.
Talking to The Hollywood Reporter, Seth Green - who lends his voice to the character - reflected on being cast to play the fan-favourite duck. "I got a call from James Gunn, who I worked with on Scooby-Doo 2: Monsters Unleashed. He said, 'I’ve already shot the colored animation for the Howard cameo but the lip assignment is pretty loose. Do you want to come in and loop these two lines for this tag on Guardians of the Galaxy?' And I said, 'Yeah.'"
"He made the second Guardians and was like, 'I threw Howard into this seedy place,' told me the line was, 'You’re out of luck, until you’ve gone duck,' and I said, 'OK, let’s try that.'"
Green will reprise the role of Howard the Duck in What If?, and while he couldn't reveal much, the actor did mention that "[it's] really cool because it resulted in a scene between T’Challa and Howard." The animated series will mark the late Chadwick Boseman's final MCU appearance, and it seems clear that getting to see the two characters interact on screen means a lot of Green.
As for Howard's future in this shared world, he couldn't say much, but did share the following.
"I like the character in the comics, and I like subversive stuff. He’s a punk rock noir detective, at least that’s the way I play it," Green explained. "I think we can all rest assured that Marvel has good plans for all their characters that are going to make sense."
It sounds like we'll just have to wait and see what happens, but assuming Howard didn't decide to stick around on Earth, it seems likely the feathered P.I. will make his return in Guardians of the Galaxy Vol. 3.