of course , He will help her...=D, but in his own twisted way
Oro is Oro so we can expect something twisted and snicky from him.
I prediction that Orochimaru will try to heal her(or orders Karin to heal her), but he won't succed or succed but she will in weakness state, so he will think about battlefield, that every strength is necessary now and Immortal, undying and with rechergable chakra body will be more sufficent then alive body, so he may kill her from few reasons:
- give her chance to fight against Madara(if she is in no state to do that, but she wants)
- shorten her suffering and pain If she is dying slowly
- think that Edo Tsunade will be more sufficent and necessary at battlefield than alive Tsunade...
- simply wanted to kill her
- boredoom
Then he will summon her via Edo Tensei and later enters battlefield with Edo Jirayia and Edo Tsunade for great twist.
Hashirama along with rest Hokages may be mad at Orochimaru for doing that, but they will have to understand and accept that this was the best way in time of wars.
Orochimaru may explain yourself that Tsunade would be useless as alive and weak because lack of chakra and just healed so he didn't want to loose more time as everyone fought against Juubi and that why he summoned her via Edo Tensei after killing her...
In short:
- Orochimaru will kill Tsunade and summon her via Edo Tensei
- Orochimaru enters battlefield with Edo Tsunade and Edo Jirayia =D