You may have to pay a higher rate for not having continuous US auto insurance coverage if you return to the United States and need to obtain insurance in the US again. It will ultimately depend upon the underwriting rules and insurance company's guidelines of the insurance company you get your auto insurance with after returning and starting up a new US car insurance policy.
You will likely lose some discounts, such as renewal discounts and without having a US insurance provider for a certain time period and there may even be some insurance companies that will choose not to insure you. Some automobile insurance companies will not write you a policy without at least six months prior insurance. Insurance coverage from a Mexican insurance provider is not something that most insurance companies feel they can verify.
If you do get rid of your US insurance be sure to not let it just lapse on its own but cancel with your insurer. If you get canceled by the insurance provider for non-payment this could also cause you problems when you once again want to obtain auto insurance in the United States.
Also if you plan on driving into the US with your Mexican auto insurance coverage then you will want to make sure this policy from Mexico has border coverage, meaning that you are covered in the United States by your Mexican insurer.
Once you are ready to get US insurance again you can come to us for an affordable auto insurance quote with companies that will insure you even after a lapse in insurance coverage.