no, assets are siloed by domain to prevent tracking, so the user will never have the font cached. I say just mirror it, if your site is down, it's down anyway, and the user will have to connect to one less domain. If you have any images at all on your site, the font is basically just the size of one more small image.
Thanks for the tip. My other point was that google is going to be faster than me so it may be an advantage.
But yes, I get what you are saying and the rationale I used initially when hosting everything was the same. I may indeed get back to that.