We can always increase how much you can divide bitcoins by quite easily, though, and it's quite possible wallets including Bitcoin Core could change to have a smaller unit like mBTC or satoshi become the main unit if we ever go that far.
That could be the answer. I haven't thought about this,but using smaller units involves price grow isn't it?
No. Using a smaller unit does not affect the price at all as it does not change the scarcity, it just makes it more divisible. It shouldn't have any major effect on the price other than increasing adoption slightly more possibly in a world where Bitcoin has become pretty big.