Unfortunately, you'll have to solve all merge conflicts again.
If you had "git rerere" enabled, it can at least have it re-solve 'both modified' conflicts for you, though you'll still have to explicitly 'add' them and it won't solve conflicts in added/removed files.
If you didn't have "git rerere" enabled yet, you can try "rerere-train.sh HEAD" https://raw.githubusercontent.com/git/git/master/contrib/rerere-train.sh