A: Legally, yes. But you must comply with ATO reporting (STP, BAS, SuperStream). Since Premier v9 cannot do STP, you are breaking ATO reporting rules if you have employees.
This is the single biggest reason businesses still use it. You bought a perpetual license (usually for $1,000–$1,500 AUD). After that, there were no monthly fees. Compare that to cloud software costing $50–$150 per month—after two years, Premier v9 had paid for itself. myob premier v9