Personally I don't see the human race dying out totally, though I think they might be in for a tough time (and are pretty likely to become just one of the many different factions competing for ground).
FakeEdit: (Ok, originally this was just gonna be a little thing, but I kinda went off on a faction lore tangent.
In general what you are seeing in-game is just the earliest settlers and scouts from the various factions. Each faction is slightly different in what you are currently seeing though, so I'll split it up by faction here lore-wise:
Mycus - The Mycus usually prefers to bring itself in through spores and marloss stuff instead of actually bringing creatures through the portals. Then, once big enough patches of spores are produces the Fungal Spires work their way up, producing larger and larger creatures for use of the group mind. Should any area begin to be sufficiently fungalized than you'll begin to see some of the bigger Mycus creatures popping up. You might also end up seeing some in places where they are going up against the other factions, or if large patches of fungus are being threatened with extermination. That said humans could survive just fine in a Mycal world with a little care or joining the Mycus directly, so it might actually be in our best interest to hope that the Fungus wins.
Triffids - Each Triffid heart is independent, no hive minds there, and they generally prefer to spread initially by carrying creatures directly through the portals while having the brought in creatures continue to reproduce in the new world. Triffid hearts often form large families of various hearts that have all sprung from the same original heart, between which they'll share resources and energy. What you are seeing now is mainly the "get-rich-quick" type of heart families, those of lesser means that see the risk of this new world as an opportunity to elevate their families in status and power. Later on, as word of this new place spreads earth is much more likely to see some expansions from the larger families, which can afford to bring in more powerful creatures through the portals to have under the control of their hearts. Triffids aren't really conducive to humans sticking around unless they join the collective (at which point you become totally subservient to a Triffid heart), so a world where the Triffids win is not a good one in the human's book.
The Goo - Generally the Goo passes through the portals itself in small quantities, at which point it bonds with nearby things in a symbiotic fashion, occasionally gathering into large slime pits if the current world is one that it can survive in. Rather than deal in actual creatures, the Goo tends to work in energy instead, using large amounts of energy to perform actions in whatever world it needs to do things in (like pumping up normal zombies into brutes, etc.). For the moment the Goo has it's main attention focused on other places, and what you are currently seeing is pretty much the "autopilot" setting for the local goo. Should it come to be that the Goo feels that it's expansion is threatened, (such as by increasing triffid/Mycus/other presence) it's very possible that it could begin to divert more energy for local consumption, allowing for things like bigger hulks, jabberwock-lookalikes being grown from single corpses instead of requiring multiple, faster goo adaptations, and so on. A Goo-won world would be one of mutants, zombies, and chaos, and while humans could probably survive I'm not sure you would be able to define them as "humans" at that point.
Mi-go - For the most part these guys don't usually have the gumption to go up against the Big 3 unless they feel rather secure in their positions. For now you are seeing mostly their scouts and researchers, but it's very likely that later they (if they feel they can take it) will strike hard for chunks of the world with massive force brought in by portal, and then try to consolidate their holds enough that the Big 3 can't be bothered to uproot them. Mi-go controlled worlds could potentially go two different ways. If we manage to convince them that we are intelligent, strong, and technologically-advanced enough to hold our own it's very possible we could become valid Mi-go provinces (controlled by a Mi-go upper and ruling class, of course) and continue average life without too many changes (assuming you don't count the fact that we would all be lower class citizens and a portion of us would be made into slaves). The other possibility is that we don't manage to convince them we are developed enough to be citizens, and they enslave us all en-masse (as opposed to just a portion of us)
Other Lesser factions - You probably won't see much more of these guys than you do right now. Should the Mi-go successfully take some chunks you might see some of them showing up in the Mi-go controlled areas as traders, tourists, and what not, but none of the rest of them really have much of a chance of taking real chunks of the planet. (Though you might see them taking places immediately linked to their worlds, ice labs for example). As noted, they don't really have a chance at taking the planet, and those areas they do take are probably not going to be the most conducive to humans.
Horrors - They've been here for years without spreading, and they aren't likely to do much changing any time soon. They will either fight their spots free of the others, be wiped out, or be assimilated accordingly; but they aren't likely to do much more than keep their own areas free of the others (and said areas are usually rather deadly to humans too).
Shadows - They're the new kid on the block. Nobody really knows much about them or what resources they have to bear, not even the other Nether creatures (they aren't from the main Nether dimension block, so this is the first time the other Nether players are meeting them too). All anybody knows about them is that they are very hard to pin down and have some very strange abilities.
Game wise once we have a good evolving world over time I'd like to see some of the bigger and tougher faction enemies start to show up for their various different reasons. (Maybe it'll help give the people who complain about no end-game something to do
).