Will the Democratic Party collapse if they don't embrace Bernieism?

[Mister Mets]

Probably not.

The Democratic party is well-positioned to win presidential elections in the future, and to be a credible force in other races.

An issue may be the impatience of voters who might not understand why things don't immediately go their way, and might freak out if Republicans win another term in the White House, even though that would be a relatively normal development.