I was just wondering why Mesc.alks and other alks do not boil off and float away with the steam while boiling and reducing?

Thanks for any help to make me understand what is happening during this process

Nope, mescaline in salt form has a boiling point that is higher than the boiling point of water so it wont evaporate with the steam, and it is pretty stable in that temperature, so you can reduce it without any problem.

is it important to have a lid on the pot when boiling the acrb in a water/vinegar mix? even though you are reducing right after. my friend wants to know.

Lid can be there or not, doesn't matter, but if you dont put the lid, be careful the water doesn't evaporate all away and burns your stuff while you're checking the nexus and smoking a joint