You can use Orchestrator for this, I did and it works great.
Step-by-Step:
1. Monitor Object (monitor for review activities changing)
Class = Review Activity
Trigger = Updated
Filter= Status - Does not equal Pending
Link Criteria:
Status from Monitor Object equals Failed or
Status from Monitor Object equals Completed
2. Get Relationship (to retrieve the parent service request)
Class = Review Activity
Object Guid = subscribe to {SC Object Guid from "Monitor Object Activity"}
Related Class = Service Request
3. Get Object (load the parent request)
Class = Service Request
Filter = SC Object Guid Equals {Related Object Guid from "Get Relationship"}
4. Compare Values (check to see if the request loaded)
Tests That = {SC Object Guid from "Get Object"} is empty
Link criteria:
Comparison result from Compare Values equals false
5. Get Relationship (get related users)
Class = Service Request
Object Guid = {Related Object Guid from "Get Object"}
Related Class = Active Directory User
From here on, there are two paths that are nearly identical. One for the affected user, one for the assigned user.
6. Compare Values (to pull users out of relationships)
Tests that {Relationship Class from "Get Relationship"} is equal to
Path One - Affected User
Path Two - Assigned To User
Link Criteria
Comparison result from Compare Values (users) equals true
7. Get Object (load the info from SCSM on the users)
Class = Active Directory User
Filter = SC Object Guid Equals {Related Object Guid from "Get Relationship"} (users)
8. Get User (Active Directory IP, to get their email address, also ensures that this is an actual live user with an actual email address)
Filters = User Principle Name Equals {UPN from "Get Object"} (user)
*** I user the UPN as groups and distribution lists do not have a UPN, only users will
9. Compare Values (here is another split in the path, used to determine if it was approved or disapproved)
Test that {Status from "Monitor Object"} is equal to Completed
Completed = Approved
Failed = Rejected
Link Criteria - Approved = Comparison result from Compare Values (Approval) equals true
Link Criteria - Rejected = Comparison result from Compare Values (Approval) equals false
10. Send Mail
Subject and message are up to you
Recipients = {email from "Get User"}
By the end of the paths, you should have four different Send Emails, an approval and rejection email for both the Assigned User and the Affected User.
Hope this helps to get you started.