The final four candidates are literally the candidates I'd expect to make it to the convention without dropping out even if they had like 80 delegates because they're all so stubborn (Bernie included btw). There would have to be a long talk in a smoke filled room for Bernie and Warren to make ammends and talk out a deal even in that case IMO.
That didn't answer the question;
Do you really see a reality where Warren wouldn't give Sanders her delegates in some type of deal for part of her platform or a seat in the administration to send Sanders over the top? Of course there would be a deal, that's the price you pay for not have the needed delegates to be the nominee.
Like, shit, Clinton made concessions to Sanders on the platform, the DNC allowed Sanders to make changes to the process when Sanders has no leverage at all to give Clinton the nomination.
It's the most obvious outcome there is in such a situation.