What would be the limit for terrain that the Roam can handle?
When you consider the price point is a lower quality suspension, what are the main problems you would notice compaired to a higher end?
The Roam can handle any kind of MUP (multi use path) dirt track, gravel road, etc that you likely want to ride it on in an urban or semi-rural environment. The kind of stuff in the video that ColonelSanders posted is no issue.
It is NOT intended for hardcore high-speed steep-grade downhill mountain biking, nor is it intended for jumping.
At the end of the day, I would not classify the suspension fork on these as "lower quality" that will lead to problems as you asked. More correctly, I would classify the Suntour NEX/NCX fork as "fit for their intended purpose". If you try to ride them on hardcore downhill mountain bike trails with jumps and 2-6' drops, yes, they will bottom out, wear and break. But then they are NOT intended for that use case, so you couldn't fault them for that.
If you ride them on bumpy, rocky dirt trails like in Colonel's video, you will have no issue. That's the kind of stuff I ride my 14 year old Sedona on and it's still going strong on its original fork without ever being disassembled or repaired. The newer forks on the Roam are even better than the 14 year old ones.
Cheers
TRJB