I've never created a Telegram bot. TryNinja made one last month.

This could actually work! I already have a list of all posts in a topic for posts made in the last 10 months. TryNinja has the same data.
@TryNinja, can you add this to your bot? You could send a notification to all users who posted in a thread when it gets trashed. Unfortunately, that will also include users who's posts are deleted (by themselves, by the creator of a self-moderated thread, or by a moderator) because there is no easy way to trace deleted posts.
I could make something myself, but I can't do notifications and this fits a Telegram bot much better.

I'm still scraping all older posts (example). This will be done around August. After that TryNinja can have the data (probably around 60 GB) to include all topics (except for hidden boards).

There's a complication though: yesterday, I posted in this topic as a warning, knowing it would get deleted after my report. The user was Nuked, and the deleted topic didn't show up in modlog. That means topics created by Nuked users should also trigger a notification, and I didn't keep track of which user created which topic. Once I'm done scraping all posts, I could get this data again by checking which user made the first post in each topic (without downloading 5.25 million topics again).

Example:
The latest deleted topic in modlog is this topic. It has posts by 2 users, chote85 and mikeywith. I don't think I've ever had a topic deleted, but I assume chote85 will get a notification. So only mikeywith needs to receive a notification. Ideally, it should include a link to his original post because it's quite a loss of his effort.

Does this help? See all unedited (or deleted) posts made by ShowOff.
I also have this planned:

Mine as mentioned above will indeed be on-demand only.