Department of State advises Americans worldwide to exercise increased caution

https://travel.state.gov/en/international-travel/travel-advisories/global-events/worldwide-caution.html

Worldwide Caution

U.S. Department of State guidance for a worldwide caution.

Would the current state of affairs qualify for cancelling the mid-terms? Is that overly cynical?

Not in the US, not a US citizen or voter. My suspicion is the answer is "no, but it is not a given that a competent supreme court which looks likely to overturn the WH exists, if they say they want to do this"

No, there is no mechanism in the US for cancelling elections. Plus elections are managed at the local and state levels anyway, so the federal government is extremely limited in what they could even do. Trump can do a lot of damage and that could potentially include attempts to ignore the election results, but there is no realistic way he actually cancels elections preemptively.