。
I wonder what would happen if I failed.
Literal
By-chance fail-[conditional-たら] how-become [deliberative-だろうか].
だろうか is the deliberative form — the questioning shape of だろう. Unlike plain question か, this form marks the question as musing or rhetorical: 'I wonder what.' どうなる ('what becomes of, how does it turn out') is the standard verb-form question for 'what would happen' — distinct from どうする ('what to do'), which asks about action.