To answer the OP: currently there are no plans for iNat to leave Twitter (or Facebook or Instagram). Yes, they all have serious problems but they are also useful avenues for outreach.
And really, we post to those platforms maybe 8-10 times a week and I sometimes retweet cool papers or projects to give them a boost, so it’s not like we’re hardcore contributers of content. IMO Twitter is still valuable for those things, as well as keeping an eye on discussion about iNat, and there’s no need to rush any decision (which, of course, is one of the main criticisms of social media).
As for Mastodon, I personally haven’t investigated it yet but it’s worth considering. Word is that they’re currently suffering some overload issues so I’m going to give them a break for the moment.
I’m going to leave this thread open for now, but as the original question has been answered, it will be closed if the conversation turns into a broader discussion about Twitter or other social media.