About 117B people have ever lived[0]. If we assume that they were all chunky and weighed 100kg, and that they all had access to time travel, then that's a total mass ~ 120e12 kg, which is 0.00000000000000006 Solar Masses (where 1SM = 2e30).
Feeding that mass into a Schwarzschild radius calculator[1], gives an event horizon of 1.78e-13 m, or about the size of 1 single atomic nucleus. The gravity would be 2.5 m/s².
The universe ain't going nowhere.
0: https://www.prb.org/articles/how-many-people-have-ever-lived-on-earth/
1: https://www.omnicalculator.com/physics/schwarzschild-radius