The ideal result here would probably be to streamline the path to citizenship, make it significantly cheaper, and get these people paying taxes as soon as possible.
I think that's a mistaken assumption. Undocumented immigrants pay far more in taxes than they get back: https://www.theatlantic.com/business/archive/2016/09/undocum...
If per chance you meant they are net contributors to the "system" that is unsupported by your citation
Pay money, but don't get the benefits of what that money buys?
I could find articles that indicated that some restaurants planned to close, eg http://www.wpr.org/madison-restaurants-are-closing-day-witho... , but nothing to suggest that even a substantial fraction of restaurants closed.
This article http://www.nbc15.com/home/headlines/Day-Without-Latinos-prot... lists nine restaurants (with multiple locations) that were closed, with no indication that were more.
Up in Canada, they straight up import workers for low end jobs, hence why at Tim Hortons up north, you will rarely if ever see a native Canadian, its nearly entirely Asians, cause they are there on worker visas. The Canadian Govt has decided their workforce should be doing something better than making coffee or baking donuts, which isn't the worst idea when properly implemented.
"I know we pay you peanuts, but at least you get to work hard."