1) If the current uptrend line breaks from the October 2011 low, that could be a confirmation that the S&P 500 is in for another 2008 type event, and could retest the 2009 low (666). The long-term trend line from the low in 1974 hits between 600-666 from July 2012 to April 2014. So that could provide some support if there's a retest. However, if you look further out from the low in 1842, it could hit the long-term uptrend at 500! This is way out of the money downside speculation I'm talking about here if reflationary policies by the Federal Reserve (QE), ECB (LTRO) and/or China fail, and there's a flight to safe haven assets like U.S. Treasuries, cash and gold, for whatever doomsday scenario you can think of.
2) If the uptrend holds and takes out the 2000 and 2007 highs, it could rally to 2,000 before breaking down if you use the 1982-1987 and 1995-2000 rallies as a template. This doesn't mean the secular bear market would end in real-terms. Gold and commodities (oil, gasoline, metals, corn, cotton etc.) could spike against the S&P, which, in the end, probably wouldn't end well for equities, the credit market and the economy, like we saw in July 2008 when oil hit $147, but XLE (energy stock ETF) broke down and the U.S. Dollar eventually spiked. History will probably rhyme in a way. I'm going to monitor the charts of commodities, sector ETFs and various correlations going forward.
Like I mentioned in the chart below, I would respect a breakout in the S&P 500, but keep an eye out for a top and a potential break below the uptrend from October, which could start a new bear market. The bull market turns 3 in March.