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.
Labor regulation has the same effect as taxes, the money just doesn't go through the government. Higher taxes and no labor regulation would have similar consequences in corporate profit-seeking decisions, because corporations are the ones paying most taxes anyway.
Besides, there is no clean separation between government and corporations, I think it is improbable that taxes are raised after getting rid of labor regulations.
Not really: taxes are percentage-based. They turn profitable transactions into marginally less profitable transactions, but stop at zero. Minimum wages and benefits set an absolute floor below which the transaction is not worthwhile.
Even if you're not upset about the loss of low-paying jobs (and that's fair), if we think everyone deserves something, getting it should not depend on finding a job.