3- Survive until they can’t maintain there overpopulation and THEY either extinct themselves or abandon the planet, leaving an opening to fill the void they left behind. They might also be killed off by a disease.
4- Awaken in secret, plan, and overthrow the more populous species that wasn’t expecting competition.
5- Just plain co-exist. Not every species will be the greedy, selfish, destroy everything and everyone else without mercy species humans are.
It has already been stated that other species will not reach galaxy stage before yours, therefore it is impossible for any species to ascend if you have not reached the galactic stage yet.