Can a non-deterministic machine merge its branches?
One view, explained by Tom here, is that nondeterministic branches work in parallel.

A more standard view, I think, is to view nondeterminism the way it is treated in physics, in logic, and in Dijkstra/Hoare style algorithm specification: at certain points, multiple continuations are possible, one of which will be taken. The 'multiple possible universes' do not exist in parallel, but they are alternative potential states of the world, alternative ways for the algorithm to continue, one of which will become reality.

So no, steps taken in one branch are not available in another branch. You either follow one branch or the other.