OK, responding to the support request here (in the future you can just post here, we'll answer it, or email, either one we'll respond to directly).
First, just quickly, as far as rendering something "in the cloud", Pixel Plow can handle most high resolution images by splitting it up into tiles across multiple machines. There are some non-tile-compatible settings in Terragen, mostly the post effects like bloom and starburst, so you'll want to be aware of that. But otherwise it can be a good solution.
Now as to why it's crashing, we definitely need to know more about your machine's hardware to get a good idea of what might be happening. But as WAS said, a 16k image is going to require a fair amount of memory, especially as AA is increased.
The fact that it hangs at the end might indicate an issue with the "GISD" pass, if that's enabled. In fact on such a high resolution GISD can take quite a while to complete, so if you haven't left it for an hour (I know, sounds like a long time), then I would wonder whether it's just been working on something and not giving feedback in the UI, which can happen on really high resolution renders.
I think the best things to do would be to monitor both memory and CPU use toward the end of the render. If the memory use is near your total system memory, that's going to cause problems. And if it seems to hang but the CPU is still being used, that might indicate it's doing work on GISD and just not updating the UI, which means you might want to try to wait it out, give it at least 30 minutes at that resolution.
As for whether the image is saved, there is an optional automatic render output to file, but it only saves once a render completes. So if it's really crashing before it finishes, nothing would have been saved unfortunately.
Hopefully you can provide some more info and we can better help you diagnose this.
- Oshyan