When you're out of money in blackjack the game gives you 500$ to start again.
Roulette also has a reset credit button with $ icon which gives you 1000$.
There's explanation for different modes of slot machines and it's standard slot machine mechanic used in casinos, But if you never played this game, I suggest watching a video about the general rules.
The VIP rooms unlock rule is that you don't need to spend your total money to unlocking them. But you have to have that amount for the room to be unlocked. So when you become poor the rooms become unreachable again.
Re-installing the game just gives you the 6000$ starter money ( separated in different games).
One suggestion to earn easy money for unlocking VIP rooms is to open Chests and playing Wheel of fortune mini games in Slot machine mode