Unfortunately in this case you are stuck doing a reload. Anytime I'm about to do a migrate import of a large/complex configuration and/or I have any suspicions whatsoever that it might fail, I perform a migrate export of the "clean" config first before running the migrate import. Restoring the "clean" copy after an import failure will still take awhile, but it sure beats the effort of a reload...
Attend my online "Be your Own TAC: Part Deux" CheckMates event
March 27th with sessions for both the EMEA and Americas time zones