I do vaguely remember some hints from Paul (not where, however) that even if the Titans were defeated, the Thargoids might instead try with a different strategy.
'Whilst the Thargoids could always change their strategy in future, I don't think we've seen the last of their invasions'. Though it wouldn't do to read too much into a one-liner forum post from June. It could simply be a hint at the Shindez invasion.
More recently, Seo Jin-Ae:
"But I can still hear the Thargoid mind. I guess they’re done with me. They’re planning something now."