If a neutrino from outer space with energy $10^20eV$ have a elastic scattering with electron...do it have higher possibility for the W-propagator to decay into top quark?
There is indeed a process similar to what you're describing that is present in the SM, but you shouldn't think about it as the W decaying so much as the electron-neutrino tunneling through a W into a top and whatever else would be present (bbar?).