Yes, Sanders should have considered running as an independent more seriously. Hilary Clinton's popularity makes it hard for Sanders to make a great deal of headway against her. Sanders could have run as an independent to get farther, however, if he cannot beat Hilary Clinton, he still could not win the election.
I believe it would not have been detrimental Bernie Sanders if he had more seriously considered a run at the presidency on the Independent party. The name of the party certainly is a descriptive for some of his views and it appears Hillary is going to overcome him on the Democratic ticket.
Independent and other third party candidates stand absolutely no chance of winning the presidency. With our messed up two party system, independents really have the short end of the stick.
At least as a Democrat, he had the support of a significant portion of the Democratic party. As an independent, he would have nothing.
In theory, it is wonderful that independents get to run for President. But the reality is that the Presidential election is Democrats against Republicans race for the finish. Sanders would have had absolutely no chance whatsoever of becoming President if he were an independent. Right now his chances might be slim, but slim in better than nothing.
Bernie's only shot at the White House was (is) to run as the democratic nominee. Independents are rarely able to wrangle enough airtime and popularity to be considered viable possibilities in the race for the White House. Although it looks like Hillary is overtaking him, Bernie never would have risen to such fame and popularity if he had decided to run as Independent.