Nope, Orochimaru was actually the weakest, Tsunade is the strongest, that point has been subtly made several times. Orochimaru thought he was the strongest because he knew a huge amount of jutsus, but that knowledge did nothing for him in the end. Jiraiya's will allowed him to both give warning to Konoha, and die the way he wanted to. Jiraiya's final conversation with Tsunade pointed out again how Tsunade is actually the strongest Sannin. Tsunade's only weakness is psychological, and that she has the ability and will to overcome. Tsunade has no doubts in herself like Jiraiya had, but nor does she delude herself that she is better than she is like Orochimaru did, she balances between the two poles, she is realistic but with a fierce will.
The elders wanted Jiraiya because Tsunade wasn't there. The moment Jiraiya suggested Tsunade they made no objections just asked him if he could find her. And when she arrived she was immediately made Hokage- no tests or challenges.
I think Tsunade might die, but she will take out all of Pein's bodies that are there before she does. She'll likely end up dying because she will have to use her regeneration ability to make the final blow. That will turn out to be one time too many using the ability and yeah I think she'll die with Sakura and Shizune in her presence after the battle. She'll have some sort of final message for both of them.