Can an employer stop paying the premiums for an employees health insurance to cut costs?

In CA, yes. This may jeopardize the entire plan, as the Insurance Companies, generally require the employer to pay at least 50% of the premium.

The employer could shop rates at http://www.quotit.net/eProGroup/login.asp?brokerID=23433638&license_no=0596610 with no obligation.

Healthy employees, no pre-exisiting conditions can shop for individual plans here http://www.quotit.net/eproIFP/webPages/infoEntry/InfoEntryZip.asp?license_no=0596610

Those with health problems would not be able to get COBRA if there is no group health plan in force. They could get HIPAA http://www.steveshorr.com/HIPAA.Rates.htm