Starting Ranked in Preseason

My friend has never played ranked before, so I was wondering what would happen if he played his first ranked games during preseason. I'm assuming if he finishes all 10 placement games it would be just like if he played during S4 (gets hit by the soft reset), but if he doesn't finish the placement matches does the soft rest still apply to him, or will the couple placement games not matter?

TL;DR: If someone unranked plays only 5 of their placement matches during preseason, what happens when S5 hits?