When do you stop ? When your stash of coins is exhausted
It helps when the whale/cartel manipulator's (aka Evan Inc's) stash of both DASH and BTC is very large compared to base of the pyramid of non-cartel (aka the float of) DASH hodlers. And your stash never shrinks if the supply of new buyers is growing faster than the base of hodlers (who could compete with the manipulator by selling).
Also the masternode scheme further reinforces this in at least two ways:
1. The hodlers are not selling because they are earning ROI paid in newly minted DASH.
2. The non-cartelized hodlers are paid less minted coins ROI than the cartel, so the cartel is continually diluting their free market competition. (This is diminishing over time as their block reward shrinks although not if transaction volume x fees is offsetting increasing)
The only way the scheme is defeated is if the supply of new buyers becomes MUCH lower than those who want to cash out. Then the cartel has to expend their stash of BTC to prop up the price. So they would instead allow the price to crash, because their goal is to obtain BTC (which can be traded for real fiat money) for this worthless token DASH which they printed out-of-thin-air for themselves.
So from the crashed price, they could buy out all the bagholders and renew the pump process again (while not losing much of their BTC stash).
So that is why I say, that at nosebleed levels, Dash is likely to have crash event at some point, especially people stop believing Dash's InstantX offers anything worthwhile (e.g. when Ethereum and Bitcoin both get instant transactions). I had already linked to the math security errors and design flaws of InstantX, but the n00bs prefer their delusion and only a competing ecosystem with the same features and more adoption will defeat their technological ignorance and delusion.
We are not quite there yet, but at another 4 - 10X the current Dash price, it is possible depending on what happens with other developments interim.
The long-term death of Dash is when some project has moved on to attain millions of users adoption and Dash offers no features that aren't already provided by that mainstream project. Then no one will buy Dash's hype any more. It will be like Steem with a crashed price and loss of speculator confidence in their ability to FOMO pump it to fools again.