Don't delete package from cache if installation fails. If the package is corrupt, hash/etags should not match the server and it'll redownload. Furthermore, if the install was actually successful regardless of a non-zero installer exit code, the cached package will be downloaded on the next Munki execution after determining that package is no longer needed.

As discussed here: https://groups.google.com/forum/?fromgroups=#!topic/munki-dev/Q5UxFOf6En8

code/client/munkilib/installer.py

@@ -859,7 +859,9 @@ def installWithInfo(
                         foundagain = True
                         break
 
-            if not foundagain:
+            # ensure package is not deleted from cache if installation
+            # fails by checking retcode
+            if not foundagain and retcode == 0:
                 # now remove the item from the install cache
                 # (if it's still there)
                 itempath = os.path.join(dirpath, current_installer_item)
@@ -1224,4 +1226,3 @@ def run(only_unattended=False):
     errcode = IOPMAssertionRelease(no_idle_sleep_assertion_id)
 
     return (removals_need_restart or installs_need_restart)
-