Evidence from multiple sources shows that before the November 5, 2024 U.S. presidential election, the Democratic Party did in fact replace Joe Biden with another nominee:

• Joe Biden became the Democratic Party’s presumptive 2024 nominee on March 12, 2024 after clinching enough primary delegates. (en.wikipedia.org)
• Following intense concerns after the June 27, 2024 debate, Biden announced on July 21, 2024 that he was withdrawing from the 2024 presidential race and would not accept the nomination, and he endorsed Vice President Kamala Harris as his preferred successor. (en.wikipedia.org)
• Harris immediately launched her own campaign and, by July 22, 2024, had secured enough delegate support to become the presumptive Democratic nominee in Biden’s place. (en.wikipedia.org)
• On August 5, 2024, in a virtual roll call of Democratic National Convention delegates, Kamala Harris was formally confirmed as the Democratic Party’s 2024 presidential nominee—months before the November 5, 2024 election. (en.wikipedia.org)

So, in the run-up to the 2024 election, Democrats effectively conducted the “hot swap” Jason described: they replaced Biden with another candidate (Harris) as their presidential nominee prior to Election Day. The prediction therefore came true.