Two creatures are blocking my one creature with menace, is there a point between declaring blockers and damage being dealt where I can destroy one blocker, making the remaining blocker illegal due to menace?
No, this doesn’t work.
Once blockers have been declared, removing creatures that are blocking a creature doesn’t make it no longer blocked. Neither does making the creature(s) blocking it no longer able to do so through addition or removal of keywords or other abilities.
For example, giving an attacking creature flying after it has been blocked doesn’t cause creatures without flying or reach that are blocking it to no longer be blocking it.
Once blockers have been declared, the creatures have basically zeroed in on each other and changing some of their abilities doesn’t make them suddenly leave the fight.