Well often what I did in the past is give like a time limit. If you greet and don't receive a response in like a week, a month, or however long you can always remove them from your list. Of course that's with the thought that they have been active (And with the potential possibility of bumping your greeting with a explanation that it may or may not have been buried)/haven't posted any "Hiatus" content. Though with that I always welcome add backs!

I myself am not a big fan of bumps, however sometimes my DMs do get pretty crazy so as long as it's respectful I'm sure the more reasonable people will understand. ^^

I hope this helps give you a few ideas or helps!