Really think he can do it?
Trump not going anywhere
Sanders how does he get on State Ballots as the two parties have Sore Loser laws
I admit that I have not done the research, but if memory serves, the deadlines for the general elections versus primaries are different, and different rules would apply to independents versus party candidates (e.g. governed by internal party rules; once a candidate flees a party, he's no longer bound by them). I believe that there's still ample time for a new nominee to get himself placed on ballots as an independent, but I do not know the exact timelines (60 days, I expect), nor the rules on a state by state basis.
Your question is certainly valid, and I'm WAY too lazy or busy (I'll select "busy") to do the in depth research required to obtain a definitive answer.
Bloomberg has spend quite a bit of money at state and local levels with anti-gun campaigns. He’s made a bunch of contacts he might be able to convert to his benefit. He’s got the money and most likely the stroke to get on enough state ballets to run.
I disagree about Trump simply because he’s tapped into what the Clinton’s would have you believe is the VRWC or more realistically, the silent majority. You can’t ignore the turnout for his events.
Sanders would have to run as an independent. He’s really not a Democrat. The key for any Democrat candidate is what happens to the super delegates when Hillary is forced out of the race? Will they transfer to the commie. Probably not.