The only potential problem would be leaving the swapfile in an inconsistent state for next time (assuming fsck syncs all its own changes, which it jolly well ought to do). If from the shell you do "swapon /swapfile" and then "swapoff /swapfile" and get no errors, everything is fine. And if everything were not fine, the worst that could happen is that you'd need to run mkswap.

Peter