I wish they hadn't cancelled the show. Then you poor fan girls and boys would all know that Wally didn't actually die. He was either portalled to an alternate dimension on a time loop, bound to eventually be sent back to where he belongs, or he would have been sent to the future, having only been gone for a few seconds when for everyone else it felt like years. Wally can't die because he takes over as the Flash when Barry Allan dies. True story.
What?!?!?! How do you know? Did Young Justice start back up?? If so, I must've missed it. If you're just theorizing, though, I kinda had a theory of my own. Wally reappears after two years, falling through a time rift, but it's only been a few seconds for him. When he heads back to his and Artemis's apartment, he discovers that's she's babysitting her niece, Lian, and Wally freaks out thinking its his until she explains. Then, of course, a cry comes from the next room and Artemis says that that one is theirs.
No, sadly, it has not started back up. This is more of my excuse then a theory, though. And I like your idea, except there are a lot of pregnant Artemis things out there. I actually have a story that takes place 20 years after Endgame where they do have a kid, but she had been in a lab.
Oh, we knew they were doing things the moment she showed up in his shirt. But, yeah, a lot of people have stories of fan art where she got pregnant before going under cover and forgot to tell him in Endgame (which, really? You'd forget to say you were carrying the child of your lover?) or that after their "reunion" she got pregnant and didn't find out until aver Wally was gone. Some of them are good, others not so much, but there are a lot out there.