I personally would be glad if China did put more restriction on rare-earth metals exports due to this whole trade dispute. It would both stop their reckless mining of it, while bringing prices sooner to what they'd eventually level out at as China becomes more developed, their wages increase, and regulations become more enforced. Yeah, it would cause a shakeup, but it's something that would happen down the line in any case and it would eventually level out.
And I'm willing to bet technology companies would still be able to produce in the interim, China isn't the only country that exports rare-earth metals. Electronics would just be a lot more expensive for a time. I honestly believe the market would respond rather quickly, though, and a lot of mines would be reopened.