Meaning is constantly being negotiated, even during the course of a single conversation, and much more so across wider linguistic communities. But the young and the old, the British and the Nigerians, the Metropolitan professional and the rural worker, those with backgrounds in the sciences and those from the humanities, even left-wingers and right-wingers, may not belong to one linguistic community in any meaningful way, despite sharing a mother tongue and perhaps even a hometown. When they speak to each other, neither uses the language they would naturally use when speaking to those they instinctively feel are 'like them.' Each seeks a form of accommodation, a way of making the communication work, with greater or lesser effort depending on how much interest they have in it. Most of us are capable of speaking with a range of styles, registers, semantic fields and even accents, according to the communicative context, and we think nothing of it.
While there are enough people in constant communication with each other in sufficiently varying groups a language will not decay; it will only change. Those changes will leave some people mildly confused while others assimilate them completely without even realizing it. But language will decay if it ceases to be used for literary or academic purposes, or if it ceases to be written at all, or if those who use it do so for a very limited range of purposes, or or if it becomes solely a literary or academic language, no longer used for real communication at all, or if the groups who use it are too small or too isolated. Then it can lose plasticity, expressive power, or comprehensibilty between groups.
The problem with trying to impose standards in language is that nobody really listens to you. For most of human history it hasn't mattered and, except in certain specific forms of communication, they don't matter very much now. Communication in everyday life is as much about seeking ways of understanding each other as it is about exchanging information. We create standards as we go,for the times when we need them.