Everyone will be buying bitcoin at that price. Bitcoin is still bitcoin and it can go even higher so these is no point to stop buying it at a high price.
People who DCA do it all the time because they keep buying Bitcoin despite the price.
Despite the price bitcoin is bought only because the long term selling price may be good and the profit would be high. The main reason is the long past charts of Bitcoin that show big changes from low price to high price and cycles that happen.
However 100k is a price that practically has not appearer in the market yet but we will have takers at that price - consider if the price remains static at that then this would be common.
Always fractional buying is possible because a Bitcoin is divisible upto 8 decimal spaces. Don't let the price on 1 whole bitcoin intimdate you.