I believe his media career would continue to expand - and he was already being well received and established in the US across several different markets. I believe his children would still follow that trajectory and work closely with him on his show/s and content.
However what is more interesting would be the ITTL relationship with his father Bob - especially given what we know the relationship between Bob and Terri Irwin was like, it wasn't pretty. Steve walked that razors edge, which goes to my next point as he would continue to balance his commercial/business/entertainment interests and and his environmentalism and conservationism - but their not mutually exclusive of course.
From what I've read he wasn't very political (in the Australian context), but he was viewed by some environmentalists as a bit of a cop out due to his involvement with tourism. Whether this gap continues to widen I don't know. But I don't personally buy the cop-out argument - he was a natural showman and did so much to bring attention to animals and the environment than so many others ever did.
Its likely he would have been anti Coal Seem Gas particularly in Queensland and New South Wales and would likely be involved in protesting against controversial projects like Adani. Though would be cool to see a David Pocock - Steve Irwin collaboration tv project.