Three years from now Bitcoin will still be most secure cryptocoin, because it is most usefull coin and thus most valued. If some coin has 1/10 value of Bitcoin it is reasonable to assume the coin is 1/10 as secure
If that happens or looks like going to happen, considering the difficulty to exchange BTC to a fiat currency, I see a huge drop of BTC price (hence more miners abundoning mining BTC) and a hugh number of BTC owners piling into alt cryptos.
A simple no is enough for this.