I've played Hero Labs quite a lot during it's run. I think a far more realistic scenario is all the remaining hero labs concepts getting cannibalized and the few things that work getting recycled into new heroes.
Pretty much everyone remaining in hero labs require a full-on gameplay rework, something that just cannot be said about any of the heroes within the main game. Raven specifically has two unique """finished""" abilities. The work required to bring them to just a passable state like the 4 released earlier this year would be a herculean task. At that point, you're practically just making a new hero, but with the added bonus of pissing off the few hyper fixated eastern european children who are attached to these janky kitbashes.
I think a big part of why Valve gave up on hero labs is this interesting dilemma. They could either make cool, interesting, fun to play concepts like Doorman, or they could put the same effort into making Wrecker somewhat playable. One generates a ton of hype, even from people who are just casually aware of Deadlock. The other doesn't generate anywhere near the amount of hype or new player interest, but gets a ton of 9 year olds to screech and scream about "volvo money grubby gamba company ruined wrecker revert rewooooork

(((((((((((".
Actually, we don't have to imagine it. It's already happened to Calico. She plays nothing like her hero labs counterpart. I knew a ton of people were pissed when that dropped into live servers. Didn't help that she was also busted as hell.
TLDR Bringing any of the hero labs heroes to passable standards requires far more effort than a new hero release with nowhere near the same hype that a new hero release would entail. It makes far more sense for Valve to just scrap them and start over from the beginning.