OK, so if I understand correctly, Pravin wants to trigger some routine
whenever a project item is about to delete and allow deletion only
if the routine completes without errors.

How you'd do this using VSIP:

1) Create a class that implements IVsTrackProjectDocumentEvents2 interface.
In the method implementing
IVsTrackProjectDocumentEvents.OnQueryRemoveFiles, you need to run your routine
and set the result flags
(of type VSQUERYREMOVEFILERESULTS) accordingly hence telling VS if the items
can be removed. You may also
want to handle other OnQuery... methods

2) Retrieve a reference to the IVsTrackProjectDocuments interface using
IServiceProvider.QueryService method. You can obtain a reference to IServiceProvider
by simply casting the
EnvDTE.DTE object given to your add-in in the OnConnection method. This is
an undocumented but legal trick which
makes using VSIP from add-ins easy.

3) Advise your listener to the IVsTrackProjectDocuments using IVsTrackProjectDocuments.AdviseTrackProjectDocumentsEvents
method.

4) ... Ask your questions if you still have problems.

To the links provided by Carlos, I may add the specific project system interfaces
mentioned in this post - you can find their descriptions
in VSIP docs.

Hope this helps.

Regards,
Dmitry Shaporenkov