Try this:
[DeleteLastSheet]
// https://www.originlab.com/doc/LabTalk/ref/Page-obj
type "This book|page has $(page.nlayers) sheet(s)|layer(s).";
int OriginalActivePageNumber = page.active;
if (OriginalActivePageNumber == page.nlayers) OriginalActivePageNumber -= 1;
page.active = page.nlayers;
//https://www.originlab.com/doc/LabTalk/ref/Layer-cmd#-d.3B_delete_the_active_layer
layer -dd;
page.active = OriginalActivePageNumber;
---
AK