If btc down will altcoin also down or will it have a future without bitcoin
The market dominance of bitcoin is currently at 41.7%. So it is the strongest currency among all other crypto currency. That is the reason why we are seeing a trend, where altcoins go down along with the price of bitcoin. But there are few altcoins as well that goes up when bitcoin goes down. In real world scenario, you can compare it with the behavior of gold. Usually when the stock market goes down, the gold price goes up because people move their funds to gold for capital protection. I have seen DigixDao and SirinLabsToken with the similar characteristics.
As of now, the current trend is much similar to what you've mentioned. But slowly we will see a reversal. Currently bitcoin is being mined and we have a stable supply in the market. But once all bitcoins are mined, we will have to rely on the external sources of supply like traders and consumers. That is the time, when we will see the reversal of trend. Some other worthy altcoins will take the position of where bitcoin is now and control the market along with its movement. But for now, you've correctly mentioned the current trend.
I will have to agree that most of the time if BTC is on dip, the majority of the alts were also on dip mode where I think BTC is very much correlated with the other cryptocurrencies in the market. You may try to check at coinmarketcap currencies in daily basis where you can observe the movement trend in the crypto market. i think that it would be great if you are planning to buy btc, it should be in a situation where btc is at dip since price is cheaper and then you should hold it for good until the pump comes to happen.