Little guide in case anyone go trough this again:
My system wasn't broken, so just making a clean grub installation was more than enough to make it work again.
Still, i have 2 questions: Is there any reason why Calamares would fail a bootloader installation? Currently i'm using a dell insipiron 15 7580 in a Windows 10 dual boot. Previously i used a HP notebook in the same configuration and never ran into any problems with a bootloader (except the times i messed with it).
Question 2: in @gohlip tutorial to reinstall the bootloader, i noticed there was some alternate options to grub, namely grub-vanilla (used in the tutorial), and grub-common, as seen in manjaro's repository. What is the difference between those 2? Grub-common is the one installed with Calamares?
Anyway, thanks so much for the help, really appreciate