Saying that Bijuu would be killed and destroyed to never come back by the Gudo Dama, is like saying humans killed by the Gudo Dama die and can't be revived via Edo Tensei. Lol.
Kishimoto via Tobirama explanation is to vague, but I think Tobirama meant all thing that shape by chakra 100% will be erase completely.
That's mean like Edo Minato case, his body is made of 100% chakra(ninjutsu) and if his body get erase by TBB completely, he cant edo revive back unless other edo summoning ritual is perform
Alive human body is compose by flesh and chakra network different from Edo body that is pure chakra. Alive human body have DNA while Edo body don't have DNA same as Bijuus body.
Also human(alive or Edo) have soul that I think is not made of chakra and TSB cant erase them although Edo body get erase, that soul is keep save inside Pure World of NV.
Edo person that get erase by TSB can be summon back by ritual because their soul is still exist
What Tobirama afraid off is, if Minato get erase by Omnyodon he can't revive back in that time and continue fighting the war.
Bijuu body is pure chakra and Edo body also is pure chakra, that is the difference between them and alive human plus soul