How Oda could answer these points, my though:
- Oden and his pride, want to die because he himself fail or because he didn´t want to make any suspect for the Beast pirates.
In that case let say Toki want to let travel Oden alongside his members to the future, who would protect Toki and his son/daughter for the case? Im sure Toki has a limit to use her skill and how many people she can send. Don´t forget if she send Oden and co in the future, Kaido would directly attack Kuri and kill Toki and co. In that case she couldn´t teleport momo and co back and Oden would just see in 20years how his family get killed off. So to not make any attention, Oden sacrifice himself in case to save his family and the Scabbards.
I think Oden want to make it sure that his Scabbards AND Family survive and get protected.
And since I believe Toki has a limit, she couldn´t save anyone, Oden probably know it and decide to make a way where he help in future but come back in the past so he can save the scabbards and his family.