Jeff,
When using folder persistence, the controls on the folder get hidden and new CTL values assigned. Technically you could still access the GRID control, but you would need to know what the new CTL value is.
In theory you should be able to find the new CTL value by taking the original CTL value and adding Fldr'theTab'StartIndex then multiplying that result by -1; where theTab is the tab the GRID was on.
Frankly though I would simply add a GRID FIND 0,0,somevariable$ on the close of the folder with the grid to get all the values from all the cells and load these into an array. It likely will be faster and easier to manage.