Hey there.
In theory – yes, if you downgrade to the lowest plan, you retain access to analysis results despite not being able to process any more analyses.
That said, this is not the intended use of SonarCloud, and I can’t guarantee that after “catching on” (or simply as the service evolves), you will maintain access to these results indefinitely. For example, it is possible (however unlikely) that a significant change in SonarCloud would require a new analysis to see data.
With that said, SonarCloud’s Web API is the preferred way of exporting data out of SonarCloud if you want to save it in another format. How to reverse engineer the Sonar Web API
Likely, we will see a feature similar to SonarQube’s Regulatory Report come to the Enterprise plan of SonarCloud in the future, which will make such saving of data for audit purposes easier for those organizations who need it.