Warren's path to the nomination is a contested convention and being the compromise candidate between the Bernie camp and the Establishment camp. Whether or not this path is even possible is debatable, but I believe this is what she is playing for.
I think she has shot herself in the foot with recent moves (painting Sanders as sexist, using a superPAC). Her campaign seems full of unforced errors, which I find really disappointing. That said, I'm not sure how Warren staying in hurts Sanders. Warren was a huge asset at the debate stage, supporting Sanders' policies and taking down Bloomberg as much as possible. From my look at the math, I think Warren staying in would only have a minor affect on the number of delegates Sanders walks away with (and Sanders + Warren delegates would be much more than Sanders alone, if she drops out).
Since so many delegates are up for grabs this month, debates will play a negligible role from here on out, so I think she's pretty much played her role, but I don't know how Tuesday will play out.
Buttigieg simply did not have a path forward. He had no minority support. He had no chance of appealing to progressive voters. He was flanked on all sides by Bloomberg, Biden, and Klobuchar. He was by far the most likely to drop out. (Though I expect to Klobuchar to drop out soon unless she massively overperforms Tuesday. She may be the Biden backup.)
I'll use California's primary as an example of how Warren staying in the race hurts Sanders. FiveThirtyEight currently has her forecasted to win, on average, 17% of the popular vote in California, with an 80% confidence interval between 12% and 22%. If she's in the lower end of that confidence interval, then she gets none of California's statewide delegates and the only thing her presence in the race does is reduce Bernie's share of the popular vote, thus netting him fewer delegates. (This works on the assumption that the majority of Warren voters would go to Bernie if she weren't in the race, which is likely the case given that they're very similar in terms of policy). Likewise, her being in the race could cost Bernie wins in several of the closer Super Tuesday primaries, including Texas, Oklahoma, Arkansas, and Virginia.
I agree that Warren appears to be playing to get the nomination in the event of a brokered convention (similar to how Ted Cruz and John Kasich stayed in the 2016 Republican race solely to attempt to prevent Trump from getting a delegate majority) but I think she needs to realize soon that getting the nomination that way would only score Trump more points to use in political attack ads; thinking about this scenario, I can already imagine the Trump campaign running ads claiming she didn't get the nomination legitimately, she robbed Sanders of the nomination, etc., not to mention alienating both Bernie voters and Biden voters. Hopefully the Democratic Party leadership also realizes that such a scenario is not conducive to a general election victory, but my view of them is quite pessimistic.