I don't understand this absolutist mindset. It doesn't have to work this way. We can have, say, the draft - an absolutely whopping restriction on civil liberties - during WWII but get rid of it when it's no longer needed.
(From a UK perspective, though I now live in the USA):
Can anyone think of a recent situation where the UK government has given back a power it has temporarily taken? This is a genuine question - I cannot. The closest was a stand taken by David Davis against 90-day detention without charge during the Blair administration (though he has since proved rather more illiberal than this position would suggest).
In the UK at least, while it might not _have_ to work that way, in practice it does.
We haven't gotten rid of it, it still exists. It just isn't being used right now. Getting rid of it would be to abolish it entirely, and instead require people to voluntarily consent in the future. (And if you can't get people to agree to it, perhaps that should tell you something.) "needed" isn't even a factor here.
An involuntary mechanism for contact or location tracing that's accessible to governmental authorities without the consent of the user is a civil rights violation, whether it's being actively used at the moment or not.
The American public exercised their power to elect politicians who'd end the draft as the Vietnam War got progressively more unpopular. It's well within our powers, if we care enough.
Is it, in fact, "well within our powers", or do you just believe it is? I don't, in general, believe "we could take this power away from government if we wanted to" is true without an existence proof.
