There's no need for an alternative plan. The government should attempt to enforce the laws that are on the books and then re-evaluate once that has been tried.
Been there, done that. As we don't have enough agents to handle total Federal enforcement, Ashcroft gave local authorities the authority (is it legal to put those two words in the same sentence...LOL!) to enforce the immigration law when they find violations. The local authorities are refusing to comply, as I posted above. We need to compel them to comply.
And yes there should be an alternative plan, we need to eliminate the "anchor babies" path to citizenship, we need to make SS cards and DLs are fraud-proof, etc. There are many things that are not on the books right now that would be effective in fighting immigration.