Well the only thing that is clear that people seem to be a bit hand wavy about what exactly is being blocked and why it is being blocked. Lets clear that up a bit.

Libra is several things, most of which will be hard/impossible to block without new laws and also blocking a large amount of currently legal things. So, blocking all of it is not a thing.

First it's an oss blockchain platform. It's similar in design to several other blockchain platforms; none of which are currently banned anywhere. Banning software is (mostly) not a thing.

Once it gets to a stable state, somebody will fire up some nodes and a Libra network comes into existence. If other blockchains are any indication, there's a good chance there will be multiple of these (e.g. testing and public). Blockchain networks don't get commonly blocked and you can legally connect to most blockchains out there from most countries. Blocking blockchain access is not a thing.

Then it is a legal entity based in Switzerland with representatives from lots of companies (though minus a few of course as of a few weeks ago). This too is nothing special. Doing business with, being a member of, or interacting with this legal entity is not subject to blocking either.

Then there are the countless financial products, tokens, etc. you can build on top of Libra, most of which are going to be similar to other stuff out there and many of which are not currently illegal or blocked in the EU or the US.

One of those things is the Libra coin. As such coins don't get blocked but the organizations that create them are subject to legislation. The controversial thing about Libra is related to how Facebook intends to implement mechanisms for controlling its value. These are in scope for legislative action.

Once all this is up and running, Facebook plans to integrate some kind of wallet type solution to do payments into their products. That would be similar to Paypal, Android Pay, WeChat, and other stuff in this space. Payment solutions as such are fine as well. Payment solutions using some kind of stable coin are also fine. Several fintech companies already do this, legally.

So, Facebook and the Libra foundation have quite a bit of wiggle room to make most of the above a reality. Yes there would be legal hurdles. The only thing that stands out is Facebook's intention to do market making (via the Libra Association) this is the bit that is controversial. When politicians say they want to ban Libra, what they are saying is that they want to ban all of it because of this market making. The reality is that they will likely try to create some legal hurdles for the market making. Facebook can then choose to work around those.

E.g., you could feasibly implement some alternate coins (simple euro and dollar stable coins like already exist on exchanges) and Facebook has already indicated that they are thinking of doing exactly that.

IMHO it is entirely likely that Facebook may give in to the political pressure to not do this given that they already are under pressure on other fronts. This would happen before they get blocked. But if they push through with this, it's very likely that the legal and political fights around this will be very lengthy. Legislation around this topic will be slow and translating the uninformed but widely spread sentiment "we don't like this" into concrete action is not likely to happen fast.