I think that might be one of those seemingly straightforward questions that's actually very nuanced, because I suspect that the combined masses of the two stars

I think that might be one of those seemingly straightforward questions that's actually very nuanced, because I suspect that the combined masses of the two stars will have a lot to say about the outcome. For a couple of Solar mass stars, I would expect... a big explosion. I can't imagine it really happening though, except in a one-in-a-<insert -illion of choice> "head-on" collision. In that case, whether it blew apart and re-settled into a star, or a nebula, or... just blew apart, would be a function of mass and momentum. In the case of slowly decaying orbits, one star usually ends up stripping most of the atmosphere from its partner, before the core eventually passes its Roche limit, breaks apart, and is accreted. In that case you get a series of Novas (not to be confused with supernovas), and a somewhat larger star when all is finally said and done. Lots of debris, occasionally very bright. It's hard to imagine a situation in which two stars "merge" without a slow process of cannibalization. Compact collapsed bodies like white dwarves, neutron stars and the rest definitely do merge, but they're so much denser than a "living" star.