Anapodoton 

an'-a-po'-do-ton Gk. "without the main clause (apodosis)."

A figure in which a main clause is suggested by the introduction of a subordinate clause, but that main clause never occurs.

Anapodoton is a kind of anacoluthon, since grammatical expectations are interrupted. If the expression trails off, leaving the subordinate clause incomplete, this is sometimes more specifically called anantapodoton. Anapodoton has also named what occurs when a main clause is omitted because the speaker interrupts himself/herself to revise the thought, leaving the initial clause grammatically unresolved but making use of it nonetheless by recasting its content into a new, grammatically complete sentence.

Examples

"If you think I'm going to sit here and take your insults..."
"When you decide to promote me to manager—when you see more clearly what will benefit this corporation—I will be at your service."