-Tobirama only has Suidanha and a Kunai as an offense here, the Kunai won't kill Kisame at all considering Samehada will just heal him, and Suidanha would be absorbed by Samehada or it'd be absorbed on contact when he fuses with Samehada.
-Tobirama's mobility becomes garbage once inside the Dome, while Kisame's only gets better, meaning he'll get caught in a matter of minutes considering his speed is worthless inside, and his markings shouldn't be too far from the area they are fighting in, meaning the Dome will encompass them.
After that its just a matter of Tobirama waiting to die, his only chance is to take him out before the Dome comes up, but with Kisame's resilience and healing ability via Samehada, its not likely if it even happens at all.