A 51% attack is currently being carried out against Ethereum Classic. ETC is currently trading at $5.05. Before February 1, 2019, ETC will at one point have a market price below $2.50. The goal of a blockchain is to maintain consensus. Once that’s gone, the value is gone.
Before February 1, 2019, Bitcoin will at one point trade below $3632, a 10% drop in value. BTC is currently trading at $4,031.13. This price drop will be caused by the fall out from the Ethereum Classic attack as more question the security of other blockchains. E.g. A large portion of Bitcoin is controlled by a small group of mining pools.