If he is not a very rare type of genius if he ever stop practicing languages he know at C2 he will certainly forget them to B levels. It's just how our brains work getting rid of unused stuff, like how people, leaving in foreign countries start to forget their native language even if they practice from time to time calling relatives. So unless he spends all his days practicing languages while not concentrating on a single one for long, he will gain proficiency in them.
It is his hobby so he is certainly happy with this activity, but I am certainly better concentrate on few.  But anyway the guy is really great and fun to watch.
Btw once I believe I saw one video with an interpreter who have known more than 5 languages and he said that after a certain number of languages you start to learn them faster just because most of them have 'similar' rules.

Well actually I didn't see anyone in my life to write in printed letters aside from fill in forms where you asked to write with printed letters. The historical reason - we are taught so in school and punished if we try to write homework in printed letters (at least in my school). The practical one is that it is really fast although it will be hard to read fast cursive later. Another one it is pretty so official certificates, diplomas and etc. are in cursive but in this case people are writing things carefully and slowly. But anyway mostly nobody use anything handwritten here apart from students' notes, visiting logs, medical prescriptions or notes of excuse.

As a native speaker I really don't know why should anyone want to learn Russian aside from pure curiosity for the country or love for this language. It is not an easy language and it have a lot of redundant grammar. Also i don't think anyone outside Russia will discuss business matters in it. But if you like how the language sounds you can't do anything about your desired to study it :) For me it was just a pure luck that English is an international language because I like it so much.