Does anyone know after Big Bang will we get reskill or we have to buy it?

I remember it expires within 1 week after you get it after logging in for the first time.

And did it say somewhere that after the patch you get three of those scrolls instead of just one?

Scroll expired 1 week upon receiving it.

You only received one, you got more scrolls by participating in the HOT TIME events. Which.. gMS doesn't.. and has never had.