You can reinstall bootman, it will overwrite the GPT header but restore the menu. However:
- This is dangerous, because only the GPT header from the end of the disk is used (no backup)
- I don't know if Windows manages to boot in such a situation
- Your bootman menu can be overwritten in several cases (when formatting or renaming a partition in Haiku, possibly just by booting Windows, not sure what they do there)
It is the solution I use at home, but not one I would recommend.
I would suggest using another bootloader which properly supports GPT (maybe GRUB?) until we gt Bootman ready for this.