Do you know what brand the RAM is? Some brands are more prone to failure than others. Also if he's supplying you with potential engineer samples, perhaps he's using some "spare" RAM, engineering sample, second-hand, whatever, which would be more likely to fail as well. Bottom line is unless you know it's new, out-of-the-packaging and from a reputable brand (of which there are many), I would sooner suspect the source of the RAM than the use of it.
Generally speaking there's no way Terragen - or any app - can be a "RAM killer". I was in the IT industry for 15 years, hardware should almost never fail due to software issues. Even maximum CPU usage for days on end should be tolerated by a properly cooled CPU. Total RAM usage (100% usage) should not cause any problems for RAM either.
The only way hardware failure could normally be influenced by software is if the hardware is not as well cooled/ventilated as it should be for the stress being put on it. Terragen does use a lot of CPU and RAM, so it's possible that if your RAM got hot due a nearby hot CPU and inadequate cooling of one or both, then it may have caused some damage, but clearly the issue is not that Terragen is causing damage, but rather Terragen is using the hardware resources of your computer to their maximum capability and the hardware is not adequately configured for that use.
It's sort of like if you have a 500hp engine in a car, but the crank shaft can only handle 100lb-ft of torque and so if you apply maximum throttle, you break the crank shaft. Did you pressing on the gas pedal break the crank shaft? Technically yes, but it's because the car was badly designed (or not designed for a 500hp engine, at least). Same thing with a computer. You can build a computer that works OK under light loads, say it's for use in a school and they only need to do web browsing and Microsoft Office. That's fine. But if you try to use the same computer to do heavy rendering it might run into problems if it doesn't have a good CPU cooler and good ventilation. Laptops are a good example of this. Doing 24/7 rendering on a laptop is generally a bad idea because their cooling systems are designed for compactness, portability, and quiet, not maximum cooling (I know that several people here on the forums do rendering on laptops, so it's possible, just not ideal).
I want to stress however that, even in the case of inadequate cooling, hardware failure should be a rarity. All modern CPUs and motherboards have overheating protection where they'll just shut down before damage is caused if they're stressed too much.
Having said all that, I really hope you do get a Ryzen CPU, that'd be awesome!