I've been living in Australia for 10 years, but I still sound like a dang Yank. "How long ya here for?" they ask. "I have no idea," I tell them.
My accent probably isn't going to change. I'd say it's because I'm too old and my brain is less plastic than it used to be, but a) my kids talk to Australians all day at school, and they still sound like dang Yanks, and b) my brain is plenty plastic, thank you.
I have noticed a few features of Strine English creeping in though. Whereas I used to go heavy on the /a/ sound (as in 'father'), I've noticed that I now lean much more toward the 'turned script a' /ɒ/. It sounds slightly more posh than the broad /a/.
And certain lexical items were bound to creep in. When someone says "Thanks," the appropriate response is "No worries," pronounced something like "Narries," depending on the register I'm trying for.
Accent adoption probably depends a lot on the extent to which you are willing to embrace the culture that the accent represents. For a long while I held Australia at arm's length because I thought I'd be living in the States again soon. But the USA seems like a bit of a zoo right now, and I wouldn't mind staying here for a while. The accent will probably follow. Plasticity permitting, of course.