It would hurt Monero users who rely on exchange wallets instead of offline cold storage.
Volume would quickly move to other exchanges such as Cryptopia, Bittrex, Shapeshift and Bitsquare. Depending on the reason Poloniex shut down, decentralized options such as Bitsquare would likely benefit the most.
No hard fork would even be considered to recover the ...
A hack of poloniex would most likely not be the end, as it has already happenend back in March 2014 (https://bitcointalk.org/index.php?topic=499580).
Poloniex took the repsonsibility and with the help of the increased volume of the new and shiny Monero that hit the exchange, it was able to refund all costumers.
The current difficulty is about 6.604 billion, not 1.617. And the block reward is about 8.63, not 14. The other parameters seemed reasonable enough.
Those changes will certainly paint a different picture.
Any number that one can come up with will likely be (significantly) wrong, because of the very high fluctuations of the market. You simply can't make a projection on several months when the price can easily vary by 5-10% in one day.
But globally, we can say that there are only short periods of time (few days/weeks) where mining is super profitable, time ...