How long can these ATH'S last before we hit another bear market.
Anyone still buying at these high costs? lol

The bullrun will be over when the bullrun of bitcoin will be turned into the bearish trend. Bitcoin as the major indicator for how long the bullish trend on altcoin market will be end.
People were buying at high cost but the price of coin goes even higher than their buy rate and what's the different? I see nothing different with it.
As long as they are feeling confidence with their money and that's not a big problem for them to invest whatever how much it is. These days people are in competition to make profit in the market.