no more than that; finishing with that and nothing further — stronger than 'それきり', implying it ended completely.
彼に会ったのは一度きりで、それっきり連絡がない。
I met him only once, and that was it — there's been no contact since.
話し合いはそこで終わり、それっきり何も変わらなかった。
The discussion ended there, and that was that — nothing changed.
彼は謝ったが、それっきりで済むような問題ではない。
He apologized, but it's not the kind of problem that can be settled with just that.
since then; ending there — indicating that something stopped from that point onward.
彼は留学してそれっきり帰ってこない。
He went abroad to study and hasn't come back since.
メールを送ったが返事はそれっきりだった。
I sent an email, but that was the last I heard.