@Rixblix
The challenge with Warren taking any job is that there is a republican governor in MA and that could impact Warrens replacement in the senate. The democrats do not want another Scott Brown kind of surprise in a special election. Howver, this time around the democrats have the former governor available so that does help.
There are some senate races that clearly show the republicans trailing especially in Wisconsin. So much so that the republican party might have to write them off and devote their resources elsewhere. Illinois is another one.
The odds still favor Warren as Sec. of Treasury. If not that she will most certainly move up through the ranks in democratic senate leadeship.
There are a lot of people around who think a Clinton/Warren ticket is too much emphasis from the NE and from states that are already easily democratic and so her potential gains are somewhat muted.