Will I be able to continue to defer from taking required RMDs from my company's 403(b) plan if it changes plans - and offers a sep IRA instead?

I am over 70 1/2 and have been told that if my company changes plans, to a SEP IRA, that my existing 403(b) plan account would no longer be "active" with the employer and that I would have to start taking RMD distributions on the 403(b) account.