Your feature branch will still point to your work. You will not lose those changes.
As plaes said, you can reset master back one with
git reset --hard HEAD^
If you want to grab some specific files from your branch without merging, you can check them out:
git checkout yourbranch -- file1 file2 etc
If you want some files from master from before the merge you can also check these out:
git checkout master^ -- file3 file4 etc
This is not ideal but it is what is needed sometimes. A merge /may/ mean that you reject some changes from either side in a merge. The best way to attain a proper merge is to:
git merge --no-commit yourbranch
from master, then run the git checkout commands from above and finally commit:
git add . -A
git commit
When you push this branch now, you will need to add the force option
git push --force
or
git push -f
Hope this helps.