It depends on what sort of freelancer you are. What is your standing with it. If you are a platinum or higher contractor with $500K+ of money earned and 10K hours in your history, you can get away with a lot of things, and support is very nice to you. If some casual client tries to threaten you, you just send the screenshot to them and client simply gets banned (and there is a provision for that in their ToS, called blackmail by a customer).
Really, Upwork will block you only if you have provably scammed your client, or engaged in criminal activity like hacking - they obviously don't want to get into legal fights so they have zero tolerance policy against that, or if they have good reasons to suspect that you drive your clients off the platform, which is also explainable (and after recent reduction of commissions, that is also very stupid to do).
Re: reduction of commissions: obviously you don't try to circumvent Upwork with a new client, because you don't trust him yet and need payment protection which Upwork provides. When you know the client though, you are already past the $10K point earnings with him and your commission lowers to 5%. You don't want to get into trouble and risk losing your primary sales channel over 5%. 'Increasing their cut, like a lot' is a NONSENSE. 20% applies to first $500 only, so it is max $50 increase of commission per client. Is that such a significant figure? That also drew out a lot of spammers. If my sales funnel got widened by 10% (and it definitely did), i'd happily shell out $50 for that. It is optimal if client acquisition cost is over $500 - and in programming, if you can scalably attract clients for $500 a pop you are going to get really rich, quickly. I'd happily pay $1000 a pop to get clients like my average client, if you can get me a couple of those per week.
I thought of and actually suggested Upwork to remove any free contacts per month, so project bid is always paid (even if cheap). For the same reason: it will drive off spammers and simplify sales, and improve client image of the platform (being a customer myself a little, it gets frustrating how much spam you get)