How long can these ATH'S last before we hit another bear market. Anyone still buying at these high costs? lol 
The question that no one can answer that consider the bearish trend can come anytime, as long as the bitcoin is still very bullish and the crypto market will be bullish too. the trend totally depends on the bitcoin.
The fact that people will always try to make money from the market and it doesn't matter how much cost for each coin that they must have paid that as long as they can enter at the right position and they can leave with decent profit caused by the recovery that might happen soon.