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Despite his failure to retain power Napoleon's return was quite significant in how it impacted post-war politics. France was supposed to retain its 1792 borders but after the hundred days ended up with 1789 borders instead. It also arguably defused an incoming confrontation between Russia+Prussia vs Britain/France/Austria over Poland. Wellington's victory at Waterloo also greatly strengthened British influence at the congress of Vienna.
What if Napoleon never returned from exile? Let's say as luck would have it, he fell from his horse on Elba and breaks one of his legs. He is still alive in 1815 but at least temporarily incapacitated in bed. How does this influence the rest of European history?