When a game you are in ends, it checks your total points, and if below 100

then it bumps you back up to 100

. It does not happen when you are eliminated. You do not have to get down to 0

.
If you go CD and someone else takes over your position, then you are no longer the player on record and will not get your points bumped back up when the game ends. But the next time you have a game end where you are still the player of record, you'll get boosted back to 100

.
But if you played a 100

game and went CD and were replaced, you'd be done and would either need to beg for a mod to reset you, or have to start a new user.