Can I sue for termination of employee if the employer knew the business was deteriorating?

Likely not. If you have an employment contract, you may have any number of potential claims. But if you were hired as an at-will employee as the business was failing and/or winding down, even if the owner knew of the deterioration, and even if s/he spurred the end, there's little you'll be able to recover, except for possibly unemployment insurance, which you should ensure you qualify for.