How does ending the drug war take away 90% of their revenue. If you legalize drugs, the cartels would become legitimate producers and corner the market through fear and intimidation.
#2 Most drugs can just as easily be produced domestically by pharmaceutical companies.
#3 Of the drugs that can't be produced domestically, the Mexican cartels are just middlemen that can be cut out entirely. There's no reason drugs from Colombia need to transit Mexico.
#4 If you're worried about Colombian cartels - see points #1 and #2.
We already went through this with alcohol and organized crime.