Once that assumption breaks you need to avoid the costs being foisted onto people unexpectedly.
Any reasonable approach is effectively a ban at that point, like paying upfront for the whole expected lifetime cost.
Yes you can get bottled LPG gas, but it is a pain – you worry about running out, you have to call up and get them to deliver it. With piped gas you just set up a direct debit for the bill and never think about it ever again.
Also, some people prefer gas heaters because it is a different kind of heat. My father replaced his wood combustion heater with a gas one, even though he already had reverse cycle air-conditioning. Maybe just using the air conditioner would have been cheaper (he already has rooftop solar–I don't think he has a battery, but could easily put one in), but it wasn't what he wanted.
For your father's gas heating, this really sounds like an emotional decision. Modern gas heating produces the same heating as reverse cycle, where air is passed over a hot bit of metal and expelled into the room. One bit of metal is heated by an enclosed and externally ventilated flame and the other bit of metal is heated by a heat pump, but the interior side is practically the same. He might be paying hundreds or thousands of dollars a year because the fan in the gas heater happens to blow the hot air more where he wanted it or more where he was used to it.
No, it literally isn't. The reverse cycle air con just blows hot air into the room–it is purely convective. The gas heater console provides radiant heating as well.
Also, the air feels different. Reverse cycle air con tends to deliver a higher volume of air at a lower temperature; gas heaters (especially if we are talking about console units as opposed to ducted systems) tend to deliver less air, but hotter air. It feels different on the skin.