If you have a sheilded ignition cable, such as one used with a CM-6 type plug, the ignition would not have been damaged by a loose plug. If you have an ignition that uses a rubber boot at the plug with a separate grounding strap it would have been damaged. In that event the hall sensor would have failed and it likely would not run at all.

Look for the problem in the high speed circuit of the carb. Sounds like something got in there blocking the passage to the venturi. When that happes the problem you describe is exactly what happens. Runs fine up to about half throttle then quits as the stick is advanced/opened further.