Software Deployment

I am currently in the process of packaging an in house application. This package is an upgrade to existing software that has been added to and amended over several years and there is no package for it despite it being installed on many pc's. The workstation upgrade has to be done in conjunction with a server side upgrade.

If either the server upgrade fails or the new client software does not work and I need to revert to the old version again is there some way that I can set the package to backup the files on install so that it can be rolled back, if needed, at a later date and replace all the files as they were prior to the install? I know this is the way in which rollback works but from what I have read it isn't clear if this is possible once the install has successfully completed due to the backed up files being deleted.

If not, can anyone suggest an alternative?

Please help.