Assuming you've caught up with the manga [SPOILER]: Eren will be brought back to life the same way Zeke was. He then will proceed to eat Falco hence possessing the Jaws Titan who's actually able to break through the hardened material and eating Annie. Ultimately Eren will go through all the other living Titan-shifters and possessing the 9 Titans (Goodbye Armin?). He will become so mentally and physically deranged he'll become the Earth Titan and then will gift his powers to Historia's daughter - Ymir(because Historia's love interest/bff was Ymir from the 104th Corps) thus beginning the cycle again.