I neglected an aloe plant for about a year without water but by the window.
It was still alive!
Quite curious about how hardy this plant is. How long can it really last without water?
There is no "exact" answer to this question, but it appears you already know the minimum it can last without water by your own unintended experiment. Though not a perfect answer, I hope the following can help you out.
Succulents need water - it's commonly known (almost to the point of being an exaggerated myth) that succulents and cacti need very little water. This is true, but all plants need water. The amount and frequency, especially for succulents and cacti, depend on a wide variety of factors including light exposure, medium and substrates, soil, drainage. Regardless, they need to be watered occasionally.
But think about their natural habitat - Consider the natural habitat of succulents. Dry and arid, these environments often go weeks, months, and (very rarely) years without a good watering. But when it rains, it pours and saturates the soil, allowing a replenishing of the succulent's stores of water.
So... As imperfect as it is, I would propose that the duration a succulent can last without water is positively correlated with soil saturation and inversely correlated with drainage and evaporation rate. I never water my succulents or aloe, and they're perfectly healthy. The rainfall, which has recently been rare in drought-stricken California, soaks the soil periodically and since mine are in partial shade that moisture stays.
My personal record, 1.5 years for a cactus that fell behind a planter out of sight, and was healthy and growing when I found it a few seasons later.
Here's a really cool video on the topic, where an "expert" says they can last years. The fact that he doesn't peg a specific time makes me think it's never been accurately documented.
A plant at my home servived for more than 5 years.
This is how it looked after 5 years. Then I removed it from the hanging and planted it in the garden.