Unless Walt agrees to come back to get them back on track.
They may not need to use threats on Walt to get him to help. If Walt is in need of someone to go after Jesse, or just muscle in general (for Hank?/cartel?), he could trade his consulting services for their “extermination” services.
I don’t think Todd and the neo-Nazis knew where the lab was. Declan’s people had Lydia blindfolded on the way there, and they knew that she and Todd worked together, so if Todd knew where their operation was, they would expect Lydia to already know. It looked like Lydia had some sort of tracking device that allowed them to follow her there from a safe distance. Todd was probably cooking elsewhere, which they may have had to abandon due to the fire.