Well, we end up with controlled borders and a mandated e-verify system so that we don't get this problem of mass illegal immigration again. We get a modernized tracking system so that the people that come
in have a forcing function to get them
out, we force our immigrant community to learn English, causing them to assimilate, and then re-shaping our immigration system to target higher-skill immigrants and stop letting in anyone with a family member state-side helps our economy grow as we Brain-Drain the rest of the world. Right now we tell computer technicians to get bent so that we can import a construction worker instead - that doesn't make any sense, and switching from the latter to the former helps us grow economically.
We additionally get these people paying
taxes (including payroll), which will help shore up our Social Security/Medicare systems a
bit (it won't save them, but it buys us a bit of wiggle-room). When they
ran the numbers (by "They", I Mean "former CBO Director Douglas Holtz-Eakin, not Rubio's people) found that we could reduce the deficit by $2.5 Trillion and increase growth by just under a full percentage point each year ($1,500 more GDP per capita).