Yes, you have to rebuild.
But in my experience (limited because I only tried this once, and I have few Zigbee devices), I didn’t have to rebuild any flows. I could ‘repair’ the devices, which means I had to put them in pairing mode, hold them close to the Homey hub etc. Devices got repaired and worked fine in their old flows iirc.
I think this is because the devices don’t actually are removed from Homey, they simply are unreachable until you repair.
[edit] I just read this about removing vs repairing 
:
Yes, annoying when useful features get removed without any explanation. I also would like to see how my Zigbee network is routed.
