'git reflog' is your friend as it keeps a history of local operations, then you can do a 'git reset --hard HEAD@{X}' where X is the point in your reflog before the rebase started.
While this is true, it's also more of a crutch. You should practice to predict, before your rebase, what conflicts your are gonna hit. And aborting a rebase is a significantly safer option. I would only recommend reflog when you rebased (on) the wrong commit and you want to undo a successful rebase.