I don't know about reinstall options for debian. I have not done that. But it does not seem like this should not be a big problem. If you save a copy of your /etc/mdadm.conf file which should specify the set up info for the RAID array and restore it after you restore the OS the array should come up with the same configuration as long as the devices it is built from still have the same device names. mdadm --assemble option should be able to re-assemble the array if there were a problem.
If you do not have mdadm.conf you can generate the info needed for it with:
mdadm --detail --scan
You might also want to run:
mdadm --examine /dev/xxx
for each of the drives that are members of the array and keep that information handy. If you are really paranoid you could disconnect the array drives while you rebuild the OS to avoid any possibility of them getting damaged and reconnect them after you are satisfied that everything is ok.
The following link is a little old but still has good info on mdadm that you might find useful: