It is possible to break a mirror as long as there is still a copy of the data.
You can for example remove zfsfool1 for the first mirror and zfsfool3 from the second one:
zpool detach /zfsfool1 zfspool
zpool detach /zfsfool3 zfspool
However, you can't remove both zfsfool1 and zfsfool2 as they hold non redundant data.