The price of BTC on the exchanges doesn't mean squat about the "health" of Bitcoin.  A price of 1 BTC= $10,000 or 1 BTC = $0.01 on MtGox only says something about the fiat value of individual BTC portfolios.  If you bought BTC @ $0.01, you might think that BTC is very much alive - despite the precipitous drop from its highs.  If you bought @ $30...well, I can understand why you might be trying to figure out when to completely give up on BTC.   The reality is this: if you hold 10,000 BTC, and can go to your local grocery and exchange 1 BTC for a 2lb chuck roast, you don't give a rat's ass about the price of BTC on some thinly traded, unregulated, foreign exchange that is run by someone in their mom's basement.

Even if the price of BTC dropped so low that the exchanges were no longer profitable and closed, BTC would still be alive as long as people accepted BTC in payment for goods and services.  Bitcoin is dead when no one sees any value in it as a medium of exchange now or in the future.  In that sense, Bitcoin may have never really been alive to begin with.

IMO, bitcoin is still in the "pre-natal" stage of life.  Maybe now that the casino aspects of BTC are fading, people may actually try to develop the utility of bitcoin beyond something that does nothing more than separate fools from their money.