FDISK /MBR does not remove the boot loader, it just puts the backup copy of the MBR over the primary copy. The MBR is just the first sector of the disk consisting of 512 bytes and is really nothing more than a pointer to somewhere else on disk where the actual boot loader code resides. Having said that, Windows only has the capability of booting other Microsoft operating systems so the need for an alternate boot loader is necessary (such as LILO, GRUB, System Commander, etc). Apparently MacOS is the same, but I do not have experience with MacOS so I can't speak for it.
If you understand the boot loader, and the boot process of each operating system in question you should have no trouble with it. And I have *never* had a case where I had to dump a partition because of boot loader problems as boot loaders only really mess with boot sectors on the partition. And I have multi booted many OSs in my time from just about every version of Microsoft OSs to many different Linux distros, to OS/2 Warp, to Solaris x86, to BE, to etc..
You do have to know what you are doing though in many circumstances. For instance, if you know what you are doing you would also know that there are other ways other than "FDISK /MBR" to replace the master boot record. For instance you can use "dd" rather than "FDISK /MBR", or just install another boot loader which will place it's own pointer code in that first 512 bytes of the disk.
The easiest way is to set up the boot loader of each OS to load said OS from the "partition" boot record (first 512 bytes of the partition that the OS resides on). Then you use a master boot loader (such as LILO, GRUB, System Commander, etc) to load each of those partitions and be the loader called from the MBR.