can you ascend to the god tier if your dreamself is dead? is it also possible if you haven't completed the echeladder, or are these things not elaborated in canon?

Yes, you can ascend to godtier if your dreamself is dead, you just have to use your Sacrificial Slab and not your Quest Bed. Everyone who has gone godtier has reached the top of their echeladder but it has not been stated outright if it is a requirement to ascend.