maybe check to see what automation is deleting your systems, and modify it so it doesnt do that anymore?
you might be able to create a Logging ->Audit Log Entries query, and have this query look for audit log entries related to system deletions. from here, you could create a server task to email you a report? thats the only way I can think of automating it. the alternative might be writing something for the sql back end to email you if the managed systems drop below a certain level?