i don't hold any of them in first place to want to decide what to do when they get dumped! we all know that sooner or later all the altcoins out there are going to get dumped so the only question is when to get in and how long to stay in.
the answer depends on the market itself and the potential of the ongoing pumps that the specific token has. then as soon as that pump ended you must make your exit instead of waiting around.
You proof your point for altcoin market are highly manipulated but if we look at the bright side of altcoin market, there are actually some altcoin which bring good returns to traders and holders and once Bitcoin reach the total 21M an altcoin will take from there.
What I'm trying to point out is that there are certain attribute we need to put into consider before panic or dump token/token because of it current down trend.