Corporations are poor stewards of our welfare, and trying to coerce them into this role (i.e. minimum wage, healthcare mandate, obligation to hold on to unneeded workers like you propose here) has the nasty side-effect of inhibiting potentially beneficial transactions (pushes employers towards automation, encourages them to split decent full-time jobs into several shitty part-time jobs to stay below eligibility thresholds, locks the lowest-value workers out of the market entirely, keeps the product category well below its potential i.e. taxis, etc).
If we think people should have at least a certain income (and I do), we need higher taxes and a stronger welfare system, not more labor regulation. If we think everyone deserves good healthcare (and I do) we need single-payer, not an employer mandate. If we think people shouldn't have to face loss of income due to economic conditions, we need to strengthen unemployment insurance, not pressure companies to keep workers they don't want or need.
Going down the path of engineering a perfect society by attaching obligations to the employer-employee relationship just disincentives employers from starting those relationships if they can help it.