Hey there! That's correct! While it may function for a time, eventually it will eventually break down and cease to function since it isn't vital to survival (as opposed to early MCU Tony Stark for instance). Essentially he'll still have the armor to act as protection from monsters and other physical/magical threats while it's in one piece, prolonged effects to exposure to the Incense will make it corrode and degrade at a faster rate. Due to the lack of technology as a whole, repairs will also be difficult-to-impossible so once something else breaks, it'll simply be a nice display piece.

We'll leave it to player discretion as to how long break down takes, but in the meantime you're absolutely free to have it malfunction, backfire, hiccup, etc however which way you'd like!