People have been doing this kind of naysaying for a very long time, since well before Tomorrow’s Harvest came out, not to mention Societas X. There is absolutely no reason to think they’re done releasing albums. They said back in 2013 they have every intention to continue releasing music and they’re liking tweets to show fans they’re still active.
Personally I think if they ever quit releasing music or decide to end the band, they’ll at least mention it in an interview.