Walt has two major arguments for Hank not taking him down.
1) Here's a few million dollars Hank.
2) Ruin the lives of his children.
Remember how low Hank got when he couldn't walk? Getting back into the investigation gave him the will to recover and go on living. I don't think any amount of money is going to sway him from the pursuit of taking Heisenberg's operation all the way down.