A new-ish, well-maintained vehicle with new tires, fresh oil change etc, if it's left dormant & undriven untouched in a residential driveway for 1 year, will it be driveable after 1 yr?
Yeah, for the most part. The other commenter is right about that battery, tho. Disconnecting the battery will help, but depending on the type and age of the battery (and temperatures in the storage area) the battery might still not last. Trickle charger might be ideal here, even just a little solar panel for it.
Gas in the tank is another thing. There might be conflicting opinions on how best to handle this, but- I would run the tank as empty as practical, then fill it up completely (so you have all fresh gas) and add a stabilizer. Most stabilizers will keep the gas good for 1-2 years. Best to make sure its an Ethanol stabilizer (like Sta-Bil 360), unless you put pure gas in. Then make sure to drive it a little so the stabilized gas gets into the whole fuel system.
Otherwise, give it a good wash and then a cover for it if you can if it’ll be outside in the elements. Depending on the storage environment, things could still start growing on it, inside and out.
Disconnecting the battery will help avoid the possibility of corrosion seeping into cables. It's probably not a huge risk in the span 12 months, but it's an easy precaution.
Diesel keeps better that gasoline but there's differences between grades of diesel aswell. I'm a prepper and I contacted a local dealer to ask about how long their diesel keeps and they told me that because their diesel doesn't contain any organic compounds(?) it should be fine for several years but ones that do might start growing algae. I re-fill my canisters once a year.
Diesel typically has a longer shelf life, so thats one benefit. A year, under optimal conditions. I believe you can still buy stabilizers meant specifically for diesel.
I would highly recommend you do not drain the fuel tank, you should leave it with a full tank to minimize the amount of room for moisture in the air to condense. Too much moisture in your tank can cause it to rust from the inside out if it's steel.
Ha, as i was typing that i considered the possibility your car might be a diesel, but decided otherwise….go figure! But ya, as the others have said, there is also diesel stabilizers, but diesel does have a longer life span. Putting a stabilizer in wont hurt anything, so personally, id put it in anyways just to be safe….