I really wonder at which point BTC investors give up and quit completely.
It depends on each investor. But I believe most of the smart investors are in the market for the long-term so they don't care about the current prices. But even if some give up there'll more investors ready to jump in at the lower prices as it could give them a perfect entry-point to maximize their profits in the long run.
but if the price goes under four digits then I might be reconsidering.
rest assured that the price won't go below 4-digits.