Should you save Vlad?
Short answer: Yes, if you want his rebel-network information. Keep more than one health segment before speaking to him and do not choose “give in to the hunger.”
How to keep Vlad alive
During Bad Blood, follow the optional trail from the soldiers near the burning house. Defeat the soldier and Vrakhiri Banneret, then convince Vlad to leave. If Coen has one segment or less, hunger forces the feeding scene and Vlad dies. With more than one segment, Coen can resist and Vlad survives.
Saving Vlad gives information about the rebel network and a later meeting. The optional rescue also reduces the later Return to Laslea and save your family cost from two segments to one.
Missable warning: Heal with Vials of Human Blood before the conversation if the miniboss leaves you below the threshold. Make a save before entering the burning house.
Sources: PC Gamer Vlad guide and PowerPyx Bad Blood walkthrough.