Switch from Single Employer to One Participant Plan

I have a client that has historically been a 5500 SF filer, consisting of a husband and wife, and one employee.  The employee left the firm in 2017 (was not replaced) and moved their money of the plan in early 2018.  In 2018, they filed a 5500 SF as a Single Employer plan because the terminated employee still had money in the plan for a portion of the year, and the plan was still covered by a fidelity bond.  For 2019, should I have them file the 5500 SF as a One Participant plan (dropping the bond requirement) or should I continue to file them as a Single Employer plan?  I still think it's easiest to have them continue to file an SF as opposed to switching to an EZ.  It's a fairly simple situation. anyone see any issues either way?

We do SF as 1 participant plan in such cases, gives you the electronic acknowledgement of filing.

Thanks Lou, I think perhaps I wasn't clear.  The issue is not really switching from an SF to an EZ, they'll continue filing an SF.  My question is really the switch from a Single Employer plan (which they have done in the past) to a One Participant plan.  Will changing which box is checked cause the IRS confusion?

Oh, yeah maybe my response wasn't clear.  We would "switch" the box from "Single Employer Plan" to "One-participant Plan" on the 2019 Form 5500-SF in this situation (since 2018 was last year it covered non-owner participant). Then complete only the fields applicable to "One-participant Plan" for 2019.

That was my first inclination as well.  Thanks Lou!