Artist's conception of the blue straggler system, actually drawn by one of the astronomers!
It's not too surprising that the collision and merger hypotheses are unlikely for blue stragglers, though they paint a more interesting mental picture.
Even in star clusters, space is woefully empty, so it is extremely unlikely that stars will ever just happen to collide. Instead of spiraling in towards each other in a violent collision, the stars tend to distort each others shape so that a stream of material can be passed from one to the other in a process called accretion.
The end result is a bit tragic as both stars are sped along to a faster death. The larger one becomes a hot blue star that burns through its fuel at a faster rate than before, and the companion gets stripped until all that remains is the leftover core, usually a white dwarf. So, the stars aren't catastrophically smashing as I always pictured. But as my friend Gail reassured me, "Bah! Smashing is involved on some level. Stars don't accrete gently."
I have the best friends.
Images: 1st – Open cluster NGC 188as seen by the 3.5-meter WIYN telescope with the blue stragglers circled. Credit - K. Garmany, F. Haas NOAO/AURA; 2nd Credit – Richard Powell and here; 3rd Credit - Maeder and here; 4th Credit – Aaron M. Geller. Gail Zasowski is an astronomer and my officemate, and one of the coolest people I know.