Tasks and policies are made in the database, not the repository so that's a little odd.
Rebuilding the repository alone should not affect the tasks and policies (Unless as part of the process you uninstalled the point-product extensions...)
Are you sure it was just the master repository which failed and nothing else ?
Perhaps if you can list out exactly what steps you took to rebuild it'll shed some light on why this has happened.
If at any stage you removed the extensions though, those associated tasks & policies are really gone.
But even then those tasks & policies should still be in any recent ePO DB backup you may have.
You might be able to build a test server up with the same ePO version, restore a backup DB then export the policies from there at least.
Those policies can then be imported back to the policy catalog. (You'll still have to reassign them to machines or groups in the system tree).
Also, make sure you check the policy catalog to confirm they really have gone and not just been unassigned somehow.