> send an IM asking if someone if they were available before interrupting them with your physical presence

Unless someone ignores IM (not even seeing notifications), sending a message is also interrupting…

If they don’t respond…they’re not available.

You can disable slack notifications. It’s great, as long as you remember to periodically check it.

I disable all notifications and just check IMs and emails every time I reach a place where that's not harmful to my work.

This needs to be relearned both in person and online.

Poor planning on someone else’s part shouldn’t make an emergency on your part.