You can check Royale Pass rules in the following ways:
1. Tap the RP button on the right side of the Lobby screen.
2. Tap the question mark (?) button right next to the ROYALE PASS logo.

There are several questions aren't mentioned in the game:

1. When will the Royale Pass expire?
Every season the Royale Pass will expire at the end of the season.

2. Can I keep those items from Royale Pass after the season is over?

The items you get from Royale Pass are permanent except for the consumables like Room Cards.

3. Will RP points reset when the Pass expires?
Yes. Please use the RP points to redeem the rewards via the Redemption page before Pass expired.