No, incorrect, he has not lost. This process is still in the early stage. Having only mostly the deep red states voted. Many presidents were at a much lower delegate count at this point and have won, Obama included.
To answer your questions, yes he could run as independent if that need does arise. Yes he could run without democratic support if that need does arise. Yes, he could still be written in regardless. No, thank God we will not need to waste 4 years with drumpf. Don't be surprised if Republicans prevent him as being the nomination as even they don't want that foolish hate monger representing them. They could, and most probably will if the need arises, have an open convention and nominate someone, anyone, but him as they know very well a drumpf presidency would have their own party in complete gridlock and could be the demise of the party completely. Even they do not want to put this country nor the world through 4 years of an awful drumpf scenario.
#BernieOrBust