Can an employer lay me off and avoid paying residual commission?

I was working as a sales representative and paid on an hourly rate + a residual commission. Most of my sales are for renewable 1 year memberships and my residual commission was an amount each month as long as those memberships stayed active and I didn't leave the company. I had the most memberships of any sales agent and received an additional monthly amount on the residual commission for every month I was the top agent. Recently the employer lost it's primary ability to generate new leads. Most sales agents quit, but I stayed on with a few other top performers with reduced hours. A few weeks later I was laid off. I still have hundreds of active memberships that I expect will continue for 2-4 years. Can my employer lay me off and avoid paying residual commission on those memberships that I've closed over the length of my employment?