Hi Bruce Martin,
I would like to clarify the following information:
1. Whether the only user needs the expired trial subscription?
2. Did the trial subscription mean the service license (such as Lync online license, SharePoint online license, Exchange online license) or Office Professional Plus service?
Based on the description, you are a single user, if you want to continue to use the Office 365 P1 Plan, at least you need buy these licenses for the single user. In other word, if the single user wants to use SharePoint Online (Exchange Online, Lync Online) service, the user need related license.
If you meant the Office Professional Plus service, it won’t affect your Office 365 P1 Plan.
Thanks,
Ida Qiu