While WebAssembly is a great new innovation, it is quite limited in what it can do so far. You'll need JS to manage a lot of things for WebAssembly still, and without a solid backing in JS, WebAssembly for the foreseeable future would be more difficult than it would need to be.
Right now WebAssembly is much more geared towards large and specialized applications -- you wouldn't use it to do anything that could also be done in JS since the size of the download would be much bigger and it would actually likely be slower due to the overhead (depending on computational complexity and throughput).
I think it'll still at least be a decade before you could develop for the web and get away with only compiling down to Web Assembly and be able to ignore JS. I'm not even 100% convinced that day will ever come that some basic JS understanding wouldn't be essential.