Do we need to bother with performance management at all before terminating?

No – not if you are prepared to spend money. Again, any employee can be let go at practically any time for practically any reason, so long as they are paid out properly and that reason is not discriminatory. You can fire an employee for the colour of their shirt, so long as you are not firing them for the colour of their skin. 

The motivation behind performance management is partially that it is intended to solve problems, but also that it gives employers a road to terminate for just cause for poor performance. That road though should never be taken lightly. It is a winding path full of hard-to-navigate obstacles, and an employment lawyer will always be your best guide.