Scenario is the same as when Dr Strange had to face him at the end of the film, except no time manipulation shenanigans to save the hero this time. It's basically just a question of how long people think they could survive, before Dormammu eventually manages to take them out. This list isn't in any specific order here, but feel free to list them in the order you think they go down.
1. Captain America (with shield)
2. Beast (all feats)
3. Spiderman (Maguire)
4. Spiderman (Garfield)
5. Spiderman (MCU)
6. Anakin Skywalker (RotS)
7. Hellboy
8. Nightcrawler (all feats)
9. Lizard (ASM)
10. The Ancient One
__________________ Never take life seriously. Nobody gets out alive anyway.
Perhaps Deadpool. Deadpool will start running his mouth, Dormammu will try to kill him a few simple ways, Deadpool will heal from being impaled or crushed or zapped and be incessantly talking the whole time, and Dormammu might eventually kick him out of the Dark Dimension just so he won't have to hear Wade talk anymore.
Or Dormammu keeps coming up with more horrific and agonizing ways to kill/maim Wade until he breaks him, but continues to torture him because that is what the Dark Dimension is all about IAW the film.
Hopefully Deadpool gets the former, not the latter.