If Romney is the nominee Heller and Brown will surely win.
I wouldn't say that. Brown is certainly moderately favored in that situation but it's not out of reach for Warren. Romney may poll better in Massachusetts than any other Republican but he's actually not at all popular in the state. If anybody other than Romney is the nominee I don't think it's very likely at all that Brown wins.
It's a college poll (from a mediocre college), understates the number of Democrats in Massachusetts, and Warren still doesn't have the world's best name recognition. I wouldn't call it
suspect but this isn't something that changes my perception of Brown's and Warren's chances.
The current registration in MA is actually 37% DEM, 11% GOP, 52% IND.
This gives us 47-43 Warren over Brown, though reweighting is...not a great measure. I think at this point the best thing to assume is that they're basically tied.