I just did an experiment which found that publish collate did not effect whether AutoCAD plotted to a single or multiple sheets.
Test: PUBLISHCOLLATE set to 1.
Result: Multiple sheet file.
Test: PUBLISHCOLLATE set to 0.
Result: Multiple sheet file.
Test: Uninitialized sheet added.
Result: Multiple sheet file without uninitialized sheet.
Test: Plot device set to "none" for one sheet.
Result: Multiple sheet file, all sheets.
Test: Plot device set to real printer for one sheet.
Result: Multiple sheet file, all sheets.
Test: Publish to: Device named in page setup. 1 sheet set to print to printer, 2 sheets set to plot to pdf, one sheet set to "none", one sheet uninitialized.
Result: Printed the sheet set to a printer, saved both sheets set to Adobe PDF in seperate files, did nothing to the uninitialized sheet and nothing to the sheet with "none" as plotter.
Test: Publish to: PDF. Publish options: Single-sheet file. 1 sheet set to print to printer, 2 sheets set to plot to pdf, one sheet set to "none", one sheet uninitialized.
Result: Printed the sheet set to a printer, saved both sheets set to Adobe PDF in seperate files, did nothing to the uninitialized sheet and nothing to the sheet with "none" as plotter.
This surprised me. That Publish to: PDF with Publish options: Single-sheet file acted exactly the same as Publish to: Device named in page setup with Publish options: Multi-sheet file.
So in the end, Publish to: PDF and Publish options: Multi-sheet file is necessary. Publishcollate is irrelevant.