Where are include statements stored in Igor.

A while back, with a particular IGOR experiment I wanted to copy some procedures containing a number of functions and macros to another experiment, and used the "Save Procure" from the file menu. I hadn't realised that later copies of the experiment would retain the link to these Procedures and any changes to the newer versions' procedures would apply. I now have these newer experiments with procedure titles ending .ipf. If I delete those .ipf procedures in the folder to which I saved them an error is thrown up by IGOR, presumably by #include statement. But where are they stored?
Include statements are stored as text in procedure windows. There is nothing hidden about them.

A procedure file can be open by an include statement or as a global procedure file or by an explicit open.

An explicit Open is File->Open File->Open Procedure, by double-clicking the file, or by dropping the file on Igor. If you do a Save As, this establishes an explicit connection to the file, the same as an explicit open.

You can see how a procedure file was opened using Procedure->Info to display the File Info dialog. You can also invoke the dialog by clicking the document icon in the lower/left corner of the procedure window.

Execute this for further discussion:
DisplayHelpTopic "Types of Procedure Files"