Just find another gale? Really?Lydia said Todd cooked 72% or 74% meth (can't remember exactly) on his first two cooks and she wanted Declan and his guys to use him in their "lab". So I'm guessing she had them killed by Todd so he can start cooking. Walt was working for Lydia for ~3months and I guess Todd was there the whole time as well since he was shown in the montage thing so he learned a bit.
Although something I don't get is why Lydia doesn't just find an actual chemist who can actually make good meth? Just find another Gale. His meth was only 3% lower than Walt's I believe. And it's odd how Todd can only make 74% meth after working with Walt all that time when Jesse was able to make 94% for the Mexican Cartel. Maybe Todd has learning difficulties.