As someone who's worked in mine closure and rehabilitation for...

As someone who's worked in mine closure and rehabilitation for years, its not quite this simple. Resources where a large amount of the stuff you dig out is sold (eg coal) results in a deficit of backfill. While you might backfill some pits, you're almost always going to be left with open holes in the ground. Alternatively, if there is enough fill, it is often uneconomical to backfill, meaning that you'll likely be left with big spoil dumps that can be challenging to rehabilitate and pose chemical issues. Essentially creating artificial mountains.

This differs for most metal mines where backfilling is more common these days and semi-expected by government (although spoil dumps can sometimes be left behind). Although they can have big acid generating issues if not managed properly, many examples of waterways being contaminated by that. With your point about potential dam water, coal pit water is often very salty and not of a suitable quality for livestock or irrigation. Sometimes you can get a few years of reasonable quality but more often than not, eventually the salt will accumulate to the point its not usable. This does vary however and the water can be left for wildlife purposes instead (if the quality isn't too bad). Revegetating also has its own challenges. Some mines do it really well but others are absolute basket cases. The Bowen basin in qld for example has a lot of material that is highly erodible and very little rehabilitation work has been done, will certainly be a big technical challenge.

Just wanted to add my context and some realities. I'm pro metalliferous and material mining for the social and economic benefits but there will always be an impact (noting that practices are improving). It can be done with an acceptable level of impact, some great examples out there, but its not a guarantee. I'll also point out that mining disturbs only 0.1% of Australia's land, which is tiny compared to a lot of other primary industries.