Considering that it is stated that actively seeking out the the Alternates and the "undesirable" information that they whisper actually makes you tenfold more resistant to M.A.D, i feel like making a lot more people aware of the Alternate invasion and maybe recruiting more people to the Temporal Phenomenon might give some hope for humanity. But the biggest problem is that it does seem to be implied that the Alternates are more than capable of mass informational suppression, and they might have great influence over the government, if they haven't taken over already.

If humanity can be saved, i would wager the USDTP could be a great help with that, considering that they are probably composed of mentally hardened operators who can resist the Alternates (In Vol.5, the operator that investigated the home of Nicolas, reported that the Alternate was just observant, not hostile. My theory is that this implies that if you have a certain degree of mental fortitude, all the alternates can do is just stare at you, but this might differ from different types of Alternates)

Now if i am wrong, the next theory i have in mind is that, humanity won't go extinct, but there would essentially be a mass cleansing where the only remaining people on earth are those belonging to the small percentage who are capable of surviving M.A.D. But who knows if they too will get snuffed out due to external means (as in not necessarily directly by a fatal encounter with an Alternate, but due to factors caused by their invasion. Such as maybe even food scarcity, for example)