We do this kind of analysis typically in the case where we're renaming or retiring a sourcetype. We look for saved object where the sourcetype is used, e.g. saved searches (alerts, reports), dashboards, macros, eventtypes etc. Here are the queries that you can use to see if your sourcetype is used in different KOs (knowledge objects) in Splunk.
Query1 (macros)
| rest splunk_server=local /servicesNS/-/-/properties/macros | table id eai:acl.owner | rename eai:acl.owner as owner | fillnull value="-" owner | map maxsearches=10000 search="| rest splunk_server=local $id$/definition | eval id=\"$id$\" | eval owner=\"$owner$\"" | where match(value,"YourSourceTypeHere\:") | table id | rex field=id ".+\/(?<search>.+)$" | table search | eval search="search=*\"`".search."`\"*"
Query2 (eventtypes)
| rest /servicesNS/-/-/saved/eventtypes splunk_server=local | search search="*YourSourceTypeHere*"| table title | eval search="search=\"*eventtype*=*".title."*\"" | table search
Query3 (Saved searches)
| rest splunk_server=local /servicesNS/-/-/saved/searches | table title eai:acl.app search eai:acl.owner | rename eai:acl.owner as owner | where match(search,"YourSourceTypeHere")
Query4 (Dashboards/Forms)
| rest splunk_server=local /servicesNS/-/-/data/ui/views | table title eai:acl.app eai:data eai:acl.owner| rename eai:data as code eai:acl.owner as owner | where match(code,"YourSourceTypeHere")
Now, there may be people who use the sourcetype in ad-hoc queries (not saved). You can query audit logs to query those. Note that audit logs are limited by retention period on _audit index and may not have all historical data. Also below query gives result only for adhoc searches where sourcetype is referred directly. If sourcetype is used in a macro or eventtype, it won't show here. Adjust the search=... clause accordingly to find those usage.
index=_audit action=search (search="*sourcetype*=*YourSourceTypeHere:*") user!="splunk-system-user" | timechart span=1d count as "#Searches" dc(user) as "#Users"
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