[SOLUTION] Couldn't re-root again after update, finally managed to
Hi ! I'd like to mention the troubleshooting I finally found to fix my case.
As a decent noob, I made the heartbleed update without protecting me against lost root, by simply flashing stock recovery and updating through stock rom (that I kept). For one month, I've been looking all over the Internet for solution, because I couldn't gain superuser access again, even though the app SuperUser was in the drawer. I tried flashing the zip, I tried to install a custom rom, I tried a NAND restore, but nothing worked.
Finally, my phone tells me I'm rooted after flashing nexusrecovery and using WinDroid Universal HTC Toolkit to root (and that installs an app called Super-utilisateur - I'm French-speaking - with a sharp icon). Sounds simple now.
I just wanted to share a solution for those in the same case. Hope it will be useful.
(and sorry for the probably numerous mistakes I made - English are my mothertongue not)
(if somebody wants more details, just ask !)