They wouldn't so much be "at standby" as "in orbit". To enable them to intercept an object, they'd have to burn hard with a lot of fuel, which means we'd have place them in orbit with a lot of fuel.

It would be more efficient to keep a rocket on standby on Earth ready to launch, since any orbital momentum we give them after launch that is not perfectly in line with their target would have to be canceled.

If we continued to develop our space tech since the 70s intercepting this would be relatively straight forward. Take for instance something like the SpaceX BFR. One of the fundamental goals is to have the rocket able to be refueled to max capacity once in orbit. That is critical as fuel is always the issue. But with this system its mobility would be immense and it would certainly be able to do things like intercept whatever this object is. There's also technologies like space sails powered by really big lasers on Earth or in orbit. And I'm sure there are countless other options which we'll learn of once we actually start progressing again.

I'll spare the NASA rant, but suffice to say it's a shame they're now spending the lions share of their budget developing a launch system that's only ambition is to provide a comparable capacity to what we had 50 years ago.

The economics of doing that with a sample size of N=1 for potential targets is...unsound.