What happens if I activate a RU + CIS game without VPN?

You die. JK

I don't know if someone actually tried it...I mean if it is illegal, a sane person won't risk getting banned or losing the game...However I am interested to know if anyone knows what are the consequences :p

you simply can't, it'll flash or whatever and stay where it is, I tried with Dark Souls I won on gameminer

only purchase restricted game --> http://steamdb.info/sub/17925/
so you should be able to activate and play the giftable copy.

Generally if it is a steam gift, and it actually activates for you without VPN, you're good to go. Why wouldn't you, not like you actually broke any rules. There can be some caveats though, for various titles even though they activate, you get things like different language options, different regional servers options (think MMOs), sometimes you may be unable to buy DLCs yourself in your own region.

This is really case by case basis. You gotta look into places like SteamDB and even then sometimes that won't be conclusive. I had X-Com EU prepurchase from RU, activated no problem, and then after release they changed the game to run only in RU region (luckily reverted later). I also heard about some titles being blocked without actual indication on SteamDB, who knows how they do that.

Can't specifically say about Tomb Raider. Again if it does activate, you should be good. If it doesn't then well you did say you can just return it without playing with VPNs.

If you have tomb raider 2013 RU. I am sure after activation, it is region free with all language supported.

«Tomb Raider» doesn't have regional or language restrictions on store description, so don't worry