After installing V11 to V12, my Mercalli Prodad 2 is missing. Do I need to re-install Prodad 2 or is it just a matter of moving some files from the V11 to V12 folders?

You shouldn’t have to do anything. I have just checked and it is still available to my Vegas 12. Are you sure you had the 64-bit version installed? Because Vegas 12 is 64-bit only, so if you used the 32-bit version of Vegas before, you may need to install the 64-bit version of third-party plugins.

Apparently my V11 was 32 bits so my previous version of Mercalli is useless now

Not necessarily. It may have very well been available in both 32-bit and 64-bit versions. I would re-run the installer and see if there's a 64-bit option. Or contact ProDad and see what you need to do to get a 64-bit version.

Bingo, you are right Edward
After re-instaling, I got option for 32 and 64 bits. I am happy again

thks