Yes, it’s a living language, but that doesn’t mean that various usages will always become common or should be accepted. In general, I’m fine with various changes, as long as the ability to communicate a concept is maintained. As such, though I’m not a fan of “they” and prefer “one” for a singular undetermined gender, I accept it, because it’s almost always clear from context what is meant, so I don’t lose any descriptive power. I continue to resist the usage of “literally” as an intensifier, because now it’s unclear if that person means literally literally or figuratively.
In this case, I wouldn’t go so far as to say someone is a moron for using dice as a singular, but I would resist the usage of such because I think a distinction between singular and plural, as with countless other nouns, is a useful distinction, particularly in a dice game where one may roll various numbers and sided dice. Especially in the case of a manual, it shouldn’t be written to be flowery, it should be written to be as unambiguous and succinct as possible.
As such, specifically to the OP, in the context of a game, “roll the dice” always means 2 or more dice, otherwise it would be “roll the die”. Yes, there is the expression “roll the dice”, which means taking a chance or gambling or whatever, but I suspect it’s origin is probably tied to a dice game like craps, or odds/evens or the like which always included more than one die.
And, quite frankly, other than perhaps when I was a kid, I don’t think I’ve heard anyone refer to a die as a dice, I certainly haven’t heard it related to a dice game. So, I’d have issue with the idea that it’s common usage. Of course, typically it seems the usage of die/dice is in dice games is usually eschewed in favor of something like 2d6, 1d20, etc.