You may create armory wallet, then make paper fragmented backup. Send fragments to several your friends or family's members. When you need to restore your wallet, collect "n of m" fragments from your friends and voila! You may also store paper backup in your deposit box in bank if you trust to bank and to your government 
Yes this could make the deal I guess.
The best thing that makes robbery obsolete is strong encryption. After a certain length has been reached (and difficulty) they would not be able to acquire your funds even if they could use all of the computing power on Earth in an attempt to crack it. With "forgetting how to access it" you mean forgetting your passphrase, or? I can't really think of good advice for 'backing up a passphrase'. Maybe you could split it into two pieces (2x2 backups) and store them somewhere as well.
Yes I mean forgetting the passphrase / password. If it's a password, I can forget it; if it's a passphrase, I have to store it somewhere... this increase the robbery chances, or the chances to lose it. Splitting it in 2 if a good idea to avoid robbery / losing it.
I dont want to find myself in that position : https://www.reddit.com/r/Bitcoin/comments/4qtigi/15_btc_reward_for_the_person_who_can_help_find/
I doubt that there's a free safebox that is actually 'safe'. I recommend paying for these services.
Yes, that's why I would like to avoid these services ^^
Yes I can have 2 trustable people. But... What's about one key on a ledger wallet (with me), one on copay for example, and one in my emails?
Wouldn't you still need to memorize multiple passwords to use all of those?Yes, but the odds to lose two passwords at the same time are smaller than losing a unique one. Specially I dont think I would forget my email password
