thanks so much for sharing this. it's incredibly important that we discuss accidents when they happen.
I agree with DWT that each of those red flags should have combined to make it a no-go. however, call me cynical, but I don't think most climbers would have moved on if there was nothing else to climb and they had driven hours to get there. although I wish I could say that I'd be smarter, I wouldn't exclude myself from that group. when you only have a few days each winter to get after it, sound judgment often gets clouded.
like mr miyagi says, "best block, no be there." if the weather has been too warm, or if there's been a drastic cold snap, just don't go. if you do, you're gonna find yourself saying "man we shouldn't be here, but this line looks so cool, and we drove all this way, and I only have two more weekends to get after it." all of a sudden the risk seems worth it. (maybe the risk is worth it to you--we're all free to take the risks we want. (just don't put others in danger with your own risks (and remember there are people who care about you, too. (ok that's enough nested parentheses.)).))
so before you even make plans, check out the weather over the week leading up to the day you're going, and the forecast for the day you're looking at. if the area you're looking at is south-facing, you know that the forecast needs to be for cloudy or very cold weather. also check out Al's ice conditions report and ask around. there's no shortage of information about popular areas.
if you feel the ice vibrating under your frontpoints, either you have a high risk tolerance and the reward is worth it to you, or you made a mistake in your analysis and should have gone bouldering. no judgment intended--I've fucked up too, and I've been lucky enough to avoid injury.