Not sure if having me as a house sitter would have left your garden any better ( than it might look after you return from your travels ). I don't have green fingers. My zen vibes might compensate for that though.
It must be tough to leave that awesome place but it's also pretty damn cool to have such a lovely paradise to get back to. The way it will look by then will be, without a doubt, a surprise, unless your house sitter / gardener / family sends you 360 degree videos while you're gone ;>)
P.S. One of the reasons why I did never seriously consider your house sitting offer, is my dad ( and his health ). I haven't seen him since June and am flying to The Netherlands in two and a half week's time. Things are more or less stable but he has pneumonia a little too often ( right now too ) and that's kind of rough for an almost 70 year old with a weak heart and progressive long fibrosis.
P.P.S. I'm sure you can relate to this, as it surely won't be easy for you to be gone from your ( mom and ) dad for such an extensive time period.