generally speaking, the drobo can still do its rebuild, if the computer is shutdown,
and if a computer is hibernated, (or shut down) then im pretty sure it wont be accessing the drobo…
however, im not sure if the computer is partly awake (but has not fully awoken while a usb device is plugged into it or for another reason), and whether it is still trying to communicate with the drobo as it tries to query any connected devices.
is your computer actually powered up (but stuck on a blank blue or black screen perhaps?) or is it still powered off and it will not power up? (if it is still off currently, then you can probably unplug the data connection cable from the drobo, and let the drobo continue its rebuilds. (im not aware of a drobo rebuild suddenly stopping and going into standby mode just because it was not connected to a computer).
im not sure what drobo model you have, but usually it can take about 1 day per 1TB of data that you have, to rebuild. if this rebuild has been going on already for a while, then it might be worth waiting a bit more for it to finish.
but if it was only started recently, and if you really need to use the computer (without the drobo) then you could check the activity light on the drobo to see if it is still being accessed. (if its not, then you could try fully powering down the laptop, and then unplugging the drobos data connection cable, before rebooting the standalone computer.
the only thing to bear in mind though (and you might have already encountered this before), is that if you usually hibernate your computer (while lightroom or something else is still already having drobo data in use or open, is that a forced reboot (or unorthodox disconnection), might cause some other hopfeully minor filesystem issues that could require a windows checkdisk (on a das drobo) later on.
(for example if my windows computer with a running drobo on it, crashes or explorer quits, then i usually reboot and run a chkdsk on my das usb drobo volumes, 1 at a time, followed by another chkdsk (or more) with the /x command, until i get the “and no errors found” message. (but only when nothing else is running or using the drobo etc)
maybe after the rebuild, it might be worth running (even on your computer as well) especially if you have been having computer forced restarts yourself anyway, because all these small issues can amount to something more in future if not dealt with sooner.