I preffer to have the same composition loaded in the two machines and a switcher, but just use one. If a crash happen, switch to the second laptop wich is allready throwing some main content, and move your controller, etc.
I try'ed using two laptops with same composition linked through osc , and used a controller to trigger different contento on two laptops using rtpmidi. But if you ask me, using that configuration just for backup is a waste of resources.
And for synchronized stuff, is easier to throw an audio signal to 2 laptops and sync with stmpe, than send osc messages all the time for just in case of..