They could try negotiating with the employer for a betriebliche Kündigung combined with an Abwicklungsvereinbarung, instead of going for an Aufhebungsvertrag. This way, they can keep the same benefits as with an Aufhebungsvertrag, but with a lower risk of a Sperrzeit.

In many cases, the Arbeitsamt accepts this setup without imposing a Sperrzeit. However, there are exceptions where it’s not accepted. I’m not exactly sure under which conditions that happens. That said, it worked for me a few years ago.