A basic question on Endeca I suppose. The scenario is we have a commerce website that running on say, ATG Search (or any other search) & we need to move to Endeca. Is it possible to just use the guided selling aspect of Endeca or is it mandatory to use the experience manager also?
A second question, if we have to use experience manager then does it mean that the page layouts of the current site would have to change or can they be retained?
The easiest way to answer this would be to speak to your Oracle Account Manager as they will be able to confirm whether you have/should license Experience Manager. Considering that, even in the most recent release of Endeca (now called Oracle Guided Navigation) you can download the Tools And Frameworks module without including Experience Manager, you do not have to use Experience Manager.
As far as your second question is concerned, if you did use Experience Manager, you don't have to push all of your page layouts through this. The biggest benefit in using Experience Manager is that it gives you more control over how you merchandise the different levels in your taxonomy but you can also do that manually.