On the subject of rival schools combining i know of one example of the sort. in 1991 two unknown hicktowns, Montezuma and Copeland Kansas, having depleted numbers in their sports programs began exploring consolidation to jointly strengthen their programs. As the board viewed the possibilities brought on by the consolidation talk soon escalated from the sports being combined into the two schools being entirely merged.
Of course former students, parents, and students (who i am told absolutely hated each other) were immediately outraged by the mere suggestion. The board decided the financial benefits outweighed the rivalry and continued exploring the consolidation(after serveral quote "blood thirsty" town meetings). Parents even threatened to move the kids away if the consolidation took place. The board was smart though, instead of continuing debates and meetings, both boards held the vote(avoiding the political mess the next elections would have been)and created the new school system South Gray.
Toward the end of the year the students picked out a new mascot (the rebel) and school colors(blue and black). Over the summer the schools were repainted and the consolidation completed.
Upon the opening season of the consolidated sports, the plan had worked. girls volleyball qualified for the state tournament (and has done so several times since), and three years in a row boys basketball(though i hate to mention the sport) earned runner-ups and one state championship(they have dropped off in the last couple of years though). The school remained 1A so they still competed in 8man football, surprisingly enough, two teams, each w/ a great history of domination, combined have never done well enough to bring home a state title. In track South Gray started out w/ and has consistently placed competitors on the state finals podium(but then again its track, so no one cares)
The rivalry between Montezuma and Copeland died quite quickly the first year(in the kids anyway). Personally, based on this example, i dont think rivalry between two towns quite holds up against the benefits of the consolidation of two financially burdened schools.