I really don't think Al is going to off him. It just seems like Torio is planning on retiring and Al is about to take over. Also, seems like the history buffs are saying Torio didn't get murdered in real life.
Yeah, not that they really have to follow true to history at all, but someone earlier in the thread mentioned what happens with him. He lived to a ripe old age in real life.
And besides that, Capone in the show likes the guy a lot, no way he would kill off Torrio. Capone already showed how loyal he was to his guys by going nuts and killing the guy who beat up his friend.