As a HRC supporter, I am 1000% fully ready to vote for Sanders assuming he is the nominee. I will (again) wait three hours in line in podunksville, Arkansas to vote for someone who has no chance of winning the state because it's that important. If someone is currently a Democrat and/or liberal and currently supports HRC but won't support Sanders (and instead abstains), then they are an idiot. Straight up.
In response to the rest of your post- yes, that's how politics works. Things CAN change quite easily (although in this case, it's unlikely to happen). Why do people care about what Sanders supporters do? Because most of us are essentially on the EXACT SAME SIDE and EVERY VOTE MATTERS. This isn't a game. It's pretty fucking important who the next President of the US is. Personally, I don't give a shit if I absolutely despise a candidate. I'm not trying to vote for someone that I can have a beer with. I want someone who represents my beliefs and will fight for them. If I have to vote for the "best case scenario" candidate, then I will. Refusing to vote and letting the absolute worst case scenario candidate win isn't heroic. It's how we end up barely losing to George W. Bush.
There are numerous Sanders supporters on GAF that have said they will vote for Clinton in the GE. Far more then those who have said they will stay home. So HRC supporters need get the fuck out of my face with the lame posts generalizing Sanders supporters as conceded as a means to feel righteous.