The Bitcoin price dump might be an issue, that make sense. Wait until the price goes upwards, large balance held there as well as Bitcoin crisis going on so wait to get a reasonable solution from support. As far, Poloniex have a bad support, no response to Tickets on time.
It was even before the dump... im waiting for one withdrawl for 3 weeks.
I cant even cancel it and trade it for something else.
If poloniex goes down, all the altcoins are going to suffer a big hit for sure (But bitcoin did survive mtgox, one exchange cant kill a crypto currency)
Many cryptocurrencies are dependent on only one exchange and those will be definitely affected with closing of it. But Bitcoin is above all of them, most of the users don't keep it on exchanges and that's really a better and safe idea.