TS should take the course of action with the greatest benefit. Basically ts already outline him self how he have 3 option.

Option 1
- Reach the sales target. Everything continue as usual.

Option 2
- Fail to reach sales target. Resign to avoid burning bridges. Focus on the future.

Option 3
- Fail to reach sales target. Refuse to resign in order to get 1-2 months more salary and perhaps remuneration for being fired.

So it comes down to one thing only.

Is the bridge you are going to burn worth 1-2months salary and the remuneration? If it is then refuse to resign. It its not then resign.