It seems that that risk is small: https://www.eff.org/deeplinks/2015/05/senate-intelligence-ch... (Paragraph four is most relevant, but 'graphs one through three also make good reading.)

Moreover, recent court cases at all levels make it clear that the Judicial system is pretty sick of surveillance methods that rely on creative interpretations of law.

If the Supremes don't get a chance to weigh in and stake this behavior through the heart, Congress will soon dismantle some or all of it, only piece the programs back together over the next few years[0].

[0] Much as Ma Bell pieced itself back together (sans Bell Labs) after the breakup.

You're most likely correct in that they would rule it illegal, though I don't think we should underestimate the court's ability to produce convoluted decisions to support the status quo. See Gonzales v Raich.

Agreed.

I think it's totally worth the risk.