I think it would be pretty cool if this HNM returned to Kuftal Tunnel. Additionally, I think it would be even better if Nasomi were to create a shadowrealm style Guivre, a more challenging version of the present day Guivre that was also a timed encounter. I think the increased difficulty over the original iteration of Guivre and the time restrictions are the key elements here, not so much the exact mechanics of retail's shadowrealm Guivre (disengage and run away every 10% hp). Given Nasomi's affinity for coding challenging wyvern NMs with time restrictions I think this is definitely in his wheelhouse. Allow it to drop the Zahak's Mail and I think this forgotten HNM will go back on everyone's radar and Kuftal tourism will increase. I realize this is unlikely to materialize but I thought it was a neat idea after reading about the doomvoid encounters and noticing that Guivre has been missing from Kuftal.