Milliongenerations:11 June 2034
Sunday, 11 June 2034 happens to be the 25th anniversary of the incorporation of the foundation Stichting milliongenerations. The organization was set up for a limited time of 25 years, so it must not survive beyond this date.
If the organization manages to survive until this time and especially if it achieved meaningful things, the weekend of 10/11 June 2034 could see some event such as a congress to celebrate this.
If necessary, other and independent organizations can take over afterwards.