In Switzerland, Bob doesn't need to go as far as reporting the illegal activity of gambling. He can file a complaint to have the situation remedied, and is also entitled to reduction of rent and/or compensation, which is arguably better than simply reporting the illegal activity. Switzerland also has decent tenant protection laws, so the landlord wouldn't likely find grounds for eviction even if they were threatened, or reported by, Bob for illegal activities.
That said, even if Bob did make such a threat, he's probably "safe". The laws require that someone attempts to make an "unlawful gain" in order for the criminal offence of extortion to occur. Since Bob is legally entitled to live in a habitable environment, he would not be in violation of this law, although certainly the landlord could try to claim that is the case. It would not cross over to extortion unless Bob did something overtly for personal gain ("give me a cut of the winnings or..."), rather than basic tenant rights.
Basically, Bob has no legitimate reason to make that kind of threat, and the landlord has no legal recourse for eviction based on such a threat. From a non-legal perspective, it'd probably be better for Bob to try and find a place to live that doesn't involve such a hypothetically shady landlord. Bob would more likely find himself a victim of an actual extortion threat rather than mere eviction.
